Title: Diamond Polish and Symmetry: Guide to GIA Terminology and Abbreviations Abstract: Every GIA diamond grading report contains an assessment of a diamond’s polish and symmetry, which are contributing factors in determining the overall quality of a diamond’s finish. In evaluating polish and symmetry, GIA considers their specific features and visibility under 10x magnification. Polish and symmetry are then rated on a scale ranging from Excellent to Poor.

	The guide below explains each polish and symmetry feature, along with their abbreviations and the possible locations of polish features on the diamond.

	Laboratory clients can view the detailed polish and symmetry assessment for each diamond they submit, by going to the Item Details in My Laboratory.

	Polish Features
Polish is graded on a scale from Excellent to Poor based on the presence and visibility of polish features at 10x magnification. The following features are considered in the polish assessment.

				Polish Feature

				Abbreviation

				Definition

				Example

				Abrasion

				Abr

				An area of minute scratches or pits along a facet edge producing a fuzzy white line instead of a sharp facet junction

				Burn

				Brn
				Dop

				Whitish haze caused by excessive heat during polishing or, occasionally, by a jeweler’s torch is listed as “Brn.”

				A burn mark caused by excessive heat at the location where the dop touched the diamond is referred to more specifically as “Dop.”

				Laser Manufacturing Remnant

				LMR

				A remnant of laser manufacturing that remains on the surface of the polished diamond; typically appears as a transparent or white groove; only considered polish when it does not penetrate into the diamond at 10x magnification.

				Lizard Skin

				LS

				A transparent, uneven texture confined to one facet caused by polishing a facet off-grain

				Nick

				Nck

				A small notch on a facet junction, usually along the girdle or at the culet

				Pit

				Pit

				A tiny opening appearing as a white dot

				Rough Girdle

				RG

				An irregular pitted or granular surface of a bruted girdle due to pits and nicks

				Scratch

				Scr

				A surface mark, normally seen as a fine white line that may be curved or straight

				Polish Lines

				Wht
				TP
				Drag line
				Polish mark

				Parallel lines left by the polishing process; may appear white (Wht) or transparent (TP). A heavy transparent polish line off a surface-reaching feature is referred to more specifically as a "drag line".

				A surface feature made during the polishing process that resembles an extra facet without a distinct or straight facet junction is referred to as a "polish mark".

 A surface feature made during the polishing process that resembles an extra facet without a distinct or straight facet junction is referred to as a "polish mark"." title="Parallel lines left by the polishing process; may appear white (Wht) or transparent (TP). A heavy transparent polish line off a surface-reaching feature is referred to more specifically as a "drag line".  A surface feature made during the polishing process that resembles an extra facet without a distinct or straight facet junction is referred to as a "polish mark"." />

	Polish Feature Locations
The location of each polish feature is specified using the following terms.

				Location

				Abbreviation

				Bezel Facet

				bez

				Chevron Facet

				chevron

				Crown Corner Step Facet

				crown corner step

				Crown

				crown

				Crown Facet

				crown facet

				Crown Step Facet

				crown step

				Culet

				culet

				Girdle

				girdle

				Half-Moon Facet

				half-moon

				Lower Half Facet

				l.h.

				Pavilion Main Facet

				main

				Pavilion

				pav

				Pavilion Corner Step Facet

				pav corner step

				Pavilion Facet

				pav facet

				Pavilion Step Facet

				pav step

				Star Facet

				star

				Table Facet

				table

				Upper Half Facet

				u.h.

Examples:

View Gallery

Symmetry Features
Symmetry is graded on a scale from Excellent to Poor based on the presence and visibility of symmetry deviations at 10x magnification. The following features are considered in the symmetry assessment.

				Symmetry Feature

				Abbreviation

				Definition

				Example

				Crown Angle Variation

				CV

				Unequal crown angles

				Crown Height Variation

				CHV

				Girdle plane not parallel to the table causing uneven crown height

				Culet Off-Center

				C/oc

				Deviation of the culet from the central position on the pavilion

				Extra Facet

				EF

				Additional facet placed without regard for symmetry and not required by the cutting style

				Girdle Thickness Variation

				GTV

				Variation of the girdle thickness at the bezel-main positions

				Lower Half Percentage
				Variation

				LPV

				Variation of lower half facet length percentages

				Lower Half Variation

				LHV

				Unequal lower half facet angles

				Misalignment

				Aln

				Displacement of the crown and pavilion facets in relation to each other

				Misshapen Facet

				Fac
				MB
				MS
				MM

				Difference in shape or size between one facet and another of the same type, or distortion of a given facet; bezel, star and main facets that are misshapen are listed more specifically as misshapen bezel (MB), misshapen star (MS) and misshapen main (MM)

				Missing Facet

				MF

				Asymmetrically missing facet

				Natural

				N

				Part of the original rough diamond’s surface that remains on the polished diamond

				Non-Octagonal Table

				T/oct
				TEV

				The table of a Round Brilliant is not a regular octagon, showing differences among the four table sizes (T/oct) or among the eight table edges (TEV)

				Non-Pointing

				Ptg
				SM
				SB
				OM
				OB

				Fully formed facet that does not reach its prescribed location (short facet) or is incompletely finished (open facet), resulting in adjoining facets not meeting at precise points; non-pointing of bezel and main facets are listed more specifically as short main (SM), short bezel (SB), open main (OM) and open bezel (OB)

				Out-of-Round

				OR

				Deviation from the circular shape of a round diamond

				Pavilion Depth Variation

				PDV

				Variation of pavilion depth

				Pavilion Angle Variation

				PV

				Unequal pavilion angles

				Star Percentage Variation

				SPV

				Variation of star facet length percentages

				Star Angle Variation

				SV

				Unequal star facet angles

				Table Off-Center

				T/oc

				Deviation of the table from the central position on the crown

				Table/Culet Alignment

				T/C

				Displacement of the table facet and culet in different directions

				Upper Half Variation

				UHV

				Unequal upper half facet angles

				Uneven Outline

				UO

				Asymmetrical shape outline; also refers to bumps and flattened areas created by a natural, extra facet or uneven girdle faceting on round diamonds

	Cumulative

	Cumulative is listed under symmetry features when the symmetry grade is based on the combined effect of symmetry features instead of individual deviations. For example, a diamond with pavilion depth variation (PDV) and crown angle variation (CV) that measures on the border of Very Good and Good may receive a lower symmetry grade based on their combined appearance and be represented as “Cumulative: PDV, CV.”

Abbreviations

				Polish Features

Abbreviation

Polish Feature

				Abr

				Abrasion

				Brn

				Burn

				Dop

				Dop Burn

				LMR

				Laser Manufacturing Remnant

				LS

				Lizard Skin

				Nck

				Nick

				Pit

				Pit

				RG

				Rough Girdle

				Scr

				Scratch

				Wht

				White Polish lines

				TP

				Transparent Polish Lines

				Drag line

				Polish mark

				Symmetry Features

Abbreviation

Symmetry Feature

				Aln

				Misalignment

				C/oc

				Culet Off-Center

				CV

				Crown Angle Variation

				CHV

				Crown Height Variation

				EF

				Extra Facet

				Fac

				Misshapen Facet

				GTV

				Girdle Thickness Variation

				LHV

				Lower Half Angle Variation

				LPV

				Lower Half Percentage Variation

				MB

				Misshapen Bezel

				MF

				Missing Facet

				MM

				Misshapen Main

				MS

				Misshapen Star

				N

				Natural

				OB

				Open Bezel

				OM

				Open Main

				OR

				Out-of-Round

				PDV

				Pavilion Depth Variation

				Ptg

				Non-Pointing

				PV

				Pavilion Angle Variation

				SB

				Short Bezel

				SM

				Short Main

				SPV

				Start Percentage Variation

				SV

				Star Angle Variation

				T/C

				Table/Culet Alignment

				T/oc

				Table Off-Center

				T/oct

				Non-Octagonal Table

				TEV

				Table Edge Variation

				UHV

				Upper Half Angle Variation

				UO

				Uneven Outline

				Polish Locations

Abbreviation

Polish Location

				bez

				Bezel Facet

				chevron

				Chevron Facet

				crown corner step

				Crown Corner Step Facet

				crown

				Crown

				crown facet

				Crown Facet

				crown step

				Crown Step Facet

				culet

				Culet

				girdle

				Girdle

				half-moon

				Half-Moon Facet

				l.h.

				Lower Half Facet

				main

				Pavilion Main Facet

				pav

				Pavilion

				pav corner step

				Pavilion Corner Step Facet

				pav facet

				Pavilion Facet

				pav step

				Pavilion Step Facet

				star

				Star Facet

				table

				Table Facet

				u.h.

				Upper Half Facet

				Modifiers*

Abbreviation

Modifier

				sl

				slight

				fnt

				faint

				hvy

				heavy

				+

				multiple

	*Reports for all diamonds graded later than January 30th, 2012 should include only the terminology and abbreviations listed in this document. You may come across non-standardized information on diamonds graded prior to January 30th, 2012 including the use of the modifiers listed in the table above.

	“Sl” and “+” were typically applied to both Polish features and Symmetry deviations, while “fnt” and “hvy” were applied exclusively to Polish features. The modifier “+” referred to multiple facets of the same type with a given polish feature, or multiple facets of the same type with a given symmetry deviation (Ex. TP: l.h.+; MM+). Source: GIA @topic:4


Title: Observations on GE-Processed Diamonds: A Photographic Record Abstract: As of august 1999, GIA staff members had examined 960 natural diamonds that had undergone a new process, developed by the General Electric Company (GE), that removes some or all of the color of a diamond. Distributed exclusively by Pegasus Overseas Limited (POL), an Antwerp-based subsidiary of Lazare Kaplan International (LKI), the diamonds are referred to as GE POL or Pegasus diamonds in the trade. These GE-processed diamonds look like untreated diamonds; however, careful examination has revealed that some of them exhibit subtle features that usually are not present in natural-color diamonds. This article presents demographic information on 858 (of the 960) GE-processed diamonds that had been incorporated into the GIA Gem Trade Laboratory database as of July 15, 1999, and describes some of the unusual internal features that were seen. As recently stated by GE, the procedure used involves high pressure and high temperature and, to date, is effective only on certain high-purity and high-clarity diamonds Source: GIA @topic:4


Title: The Wittelsbach-Graff and Hope Diamonds: Not Cut from the Same Rough Abstract: Two historic blue diamonds, the Hope and the Wittelsbach-Graff, appeared together for the first time at the Smithsonian Institution in 2010. Both diamonds were apparently purchased in India in the 17th century and later belonged to European royalty. In addition to the parallels in their histories, their comparable color and bright, long-lasting orange-red phosphorescence have led to speculation that these two diamonds might have come from the same piece of rough. Although the diamonds are similar spectroscopically, their dislocation patterns observed with the DiamondView differ in scale and texture, and they do not show the same internal strain features. The results indicate that the two diamonds did not originate from the same crystal, though they likely experienced similar geologic histories. Source: GIA @topic:4


Title: Slow Diamond Market Puts Miners Under Pressure Abstract: Rough diamonds still remain too costly to manufacture profitably, say dealers, putting pressure on the major producers. Photo by Russell Shor.

                      The soft conditions in the world diamond industry are making their way into miners’ bottom line. De Beers’ sales for the first half of the year were down 26% as clients deferred and outright refused a significant percentage of sight allocations.

This continued for the July 13-17 sight, originally planned at $600 million then reduced to about $450 million. Most clients refused or deferred unprofitable goods, bringing the total to less than $300 million.

De Beers held the line on prices in July.

While De Beers is nowhere near the monopoly it was 15 years ago, it still commands a major market share of the one carat-plus market. The company has reduced sales reluctantly – mainly because buyers have refused or deferred allocations – and has not significantly lowered prices.

Alrosa, the largest diamond producer by volume (second by value), also held the line on prices and allowed clients to defer up to 30% of their allocations. It noted that its first-half rough sales were also 26% below last year’s levels with prices down about 7%.

Tender auction sales by other producers have been running 15-25% below last year’s levels, though rough prices have receded only a few percentage points.

Mega diamonds remain the exception. Lucara Diamond Corp., which operates the Karowe Mine in Botswana, reported very strong prices at its July tender, largely from a 341.9 carat (ct.) Type IIa diamond that brought a winning bid of $20.55 million and a 269.7 ct. diamond that sold for $16.54 million. Both exceeded $60,000 per carat.

Further down the diamond pipeline, two large manufacturing operations closed in Surat, leaving obligations of more than $140 million. As reported earlier, manufacturing volumes have decreased by about one-third, causing a number of contract cutting shops in India and China to close.

While U.S. diamond and jewelry sales have edged into positive territory for the first time this year (May was up by 0.5% from 2014), China’s economic situation continues to deteriorate, which is reflected in its retail jewelry sales.

Chow Tai Fook, China’s largest retail jewelry operation, reported a 15% drop in same store sales for the quarter that ended June 30, the fourth such double-digit decline in a row. Most of the problem is centered in Hong Kong and Macau where tourist traffic is considerably off. Mainland China sales, however, are also lower – with “Gem-set” pieces running 4% down.

Another large Hong Kong based chain, Luc Fook, recorded a 20% drop in same store sales for the quarter.

Indeed, China’s diminishing economic growth is causing considerable volatility in prices and reduced demand for many commodities, causing some mining companies – which two or three years ago could not keep up with demand – to retool their operations. Prices for copper, coal, iron ore, platinum and rare earths used in manufacturing electronics have fallen sharply this year.

In Japan, the country’s ageing population, coupled with low economic growth and stagnating economy, has resulted in a major diamond sell-off. The government noted that polished diamond exports – mainly goods sold by consumers – increased 77% during the first four months of this year. The government estimates the market for “recycled gold and diamonds” at $12 billion this year, according to a Bloomberg report.

The Yen has fallen 18% against the dollar this year, which pushes up the cost of diamonds and gold in local terms and deters demand for new diamond pieces.

De Beers and other forecasters are looking for the market to pick up this fall for the September Hong Kong show and the run-up to the U.S. holiday season. Source: GIA @topic:8


Title: Characterizing Natural-Color Type IIB Blue Diamonds Abstract: Although rarely encountered, blue diamonds are among the most famous, and most distinctive, of fine gemstones. To better understand these unique gems, more than 400 were studied at the GIA Gem Trade Laboratory over several years to reveal additional information about the relationships between their color, clarity, and other gemological properties. The overwhelming majority of natural-color blue diamonds are type IIb. The color appearance varies widely from light to dark, but there is a limited range of color saturation. As a result, color appearance between neighboring GIA GTL color grades can be subtle. Of the blue diamonds examined at GIA GTL, few had any solid inclusions. Nevertheless, internal features such as graining and color zoning can make the processing of these diamonds a challenge. Source: GIA @topic:4


Title: Color Grading “D-to-Z” Diamonds at the GIA Laboratory Abstract: Since its introduction in the early 1950s, GIA’s D-to-Z scale has been used to color grade the overwhelming majority of colorless to light yellow gem-quality polished diamonds on which laboratory reports have been issued. While the use of these letter designations for diamond color grades is now virtually universal in the gem and jewelry industry, the use of GIA color grading standards and procedures is not. This article discusses the history and ongoing development of this grading system, and explains how the GIA Laboratory applies it. Important aspects of this system include a specific color grading methodology for judging the absence of color in diamonds, a standard illumination and viewing environment, and the use of color reference diamonds (“master stones”) for the visual comparison of color. Source: GIA @topic:4


Title: Retailers, Diamond Trade Still Vying Over Prices Abstract: The octahedron rough weighs 15.98 carats; the faceted diamonds are between 3.00 and 3.50 carats. Photo by Robert Weldon/GIA

	The tug-of-war between retailers, diamond miners and manufacturers over prices continues even as the world economy slowly improves.

	A number of diamond price monitoring services reported that diamonds have given up most of the price gains made earlier in the year. Additionally, Blue Nile Chief Financial Officer David Binder, speaking in a news conference announcing first quarter results, said that consumers are resisting paying high prices for polished, making it difficult for diamond manufacturers and wholesalers to pass on their increased costs.

	The pressures on middle-class consumers have been well-reported and have affected retail demand for many products, including jewelry. However, one recent report notes a growing caution among U.S. luxury buyers as well.

	Unity Marketing’s survey of luxury buyers – who have driven the increase in diamond and jewelry buying in the U.S. over the past several years – found that those consumers plan to hold the line on spending, putting more of their discretionary funds into investments and savings.

	Online retailer Blue Nile reported its first quarter sales rose 6.8 percent compared to the previous year, with its strongest business being its core engagement ring pages. However, this is below the average of about 11 percent growth the company has reported in each of the past four years.

	Press reports from China indicate that retail jewelry sales continue to slow from the heady growth of previous years. These year-on-year comparisons of retail results may not accurately reflect the market as last year’s steep drop in the gold price created a buying spree that caused an abnormal spike in sales. However, diamond dealers and manufacturers noted that Chinese retailers have begun trading down on quality to hold the line on prices as consumers there grow more cautious.

AUCTIONS: Consumer reticence does not appear to be having an effect on the extreme top end of the market, as recent jewelry auctions continue to command extreme prices.

	Sales at Christie’s April 19 New York auction totaled $60.6 million. Major items included a pair of GIA-graded round brilliant, D color, Internally Flawless diamonds, a 22.6 carat and 22.31 carat, which brought $8.56 million; and a 40.43 carat, D color, potentially Flawless GIA-graded oval-cut diamond which brought $7.7 million, or nearly $190,000 per carat.

	On April 29, William Doyle Galleries in New York sold a pair of natural drop pearls believed to have been owned by Empress Eugenie of France for a record auction price of $3.3 million. The same day, Sotheby’s New York sold a 28.18 carat Kashmir sapphire for $5.09 million, or $180, 731 per carat, a world record price for such a stone.

	As reported last month, on April 6 in Hong Kong, Sotheby’s sold the jade-bead Hutton-Mdivani necklace for a record $27 million, double its pre-sale estimate and the record auction price for a jadeite jewel. The piece contained 27 “high-translucent” jade beads, ranging from 15.4 to 19.2 mm.

	The week of May 12 will feature two major auctions in Geneva. On May 13, Sotheby’s will offer the 100.09 carat Graff Vivid Yellow Diamond, expected to sell for $15 to $25 million, and the 31.34 carat D, potentially flawless Victory Diamond, which carries a pre-sale estimate of $5 to $8 million.

	On the following day, Christie's will offer a 13.22 carat Fancy Vivid Blue diamond, named “The Blue,” the largest Flawless, Vivid Blue diamond to come up for auction (the 27.64 carat Heart of Eternity is the largest known Fancy Vivid Blue), which it expects to sell for $25 million; and the 5.5 carat Fancy Vivid bluish green The Ocean Dream, the largest vivid blue-green diamond ever to be auctioned. It is expected to bring between $7 and $10 million. Source: GIA @topic:8


Title: Online Diamond Sales 17% of U.S. Market Abstract: A recent De Beers study noted a 7% increase for diamond jewelry in the U.S. during 2013 and a 12% increase in China. Photo by Robert Weldon/GIA.

              A recent De Beers study reported that worldwide retail sales of diamond jewelry totaled $79 billion in 2013, up $5 billion on a 7% increase in U.S. demand and a 12% increase in China.

Online sales of diamond jewelry comprise about 17% of the market in the U.S., according to the study. These sales include both strictly online companies such as Blue Nile and traditional retailers who also sell over the Internet.

The De Beers report also noted that 25% of Chinese consumers now research prospective diamond purchases online before making an actual purchase and that the number of retail stores selling diamond jewelry increased 30% from 2010 to 2013. There are, however, strong signs that the heady growth is beginning to slow, according to De Beers. Retailers in Guangdong Province reported that sales declined 5.1% for the first eight months of 2014, while sales of gold pieces nationwide fell 9.1% during that period, according to a government report.

In the U.S., the Department of Commerce reported that jewelry and watch sales from all sales channels increased 4.9% in August, compared to the same month in 2013. This rise reflects even greater sales volume because prices for gold and diamonds declined several percentage points in 2014.

De Beers noted that diamond production increased 7% to 145 million carats, still well under the 2005 peak of 175 million carats. It also predicted that production would decline, despite new sources coming on stream, because older mine deposits are becoming more costly to work as operations go deeper and ore grade declines. Source: GIA @topic:8


Title: CVD Synthetic Diamond with Fancy Vivid Orange Color Abstract: Figure 1. This 1.04 ct round was identified as a CVD synthetic diamond. Its Fancy Vivid pinkish orange color was introduced through post-growth irradiation and annealing. Photo by Sood Oil (Judy) Chia.

              With the rapid improvement of CVD synthetic diamond quality in recent years, various colorations can be introduced after growth. The New York laboratory recently tested a CVD synthetic with a very attractive orange color.

This round-cut specimen weighed 1.04 ct and was color graded as Fancy Vivid pinkish orange (figure 1), a very rare color among natural and treated diamonds. Except for a few dark pinpoint inclusions, it showed no notable internal features. Under crossed polarizers, it displayed natural-looking “tatami” strain patterns. Absorption spectroscopy in the infrared region showed typical type IIa features, with no detectable defect-related absorption. At liquid-nitrogen temperature, a few absorption features were detected in the UV-Vis-NIR region (figure 2). The major ones include absorptions from N-V centers with ZPL at 575.0 and 636.9 nm, and their related side bands. We also recorded absorptions from some irradiation-related defects, including 594.4 nm, GR1 at 741.2 nm, ND1 at 393.4 nm, and the general radiation absorption features at 420–450 nm. Also observed were weak absorptions from the H3 defect at 503.2 nm, possible nickel-related defects at 516.1 nm, and [Si-V]– at 736.6/736.9 nm. Under the strong short-wave UV radiation of the DiamondView, the sample showed very strong red fluorescence with sharp linear growth striations, a unique feature of CVD synthetic diamond. Weak red phosphorescence was also detected. These observations confirmed that this was a CVD synthetic diamond with post-growth treatments. Nitrogen concentration, based on absorptions in infrared absorption spectroscopy, was below 1 ppm. After initial growth, the sample was artificially irradiated and then annealed at moderate temperatures to introduce the N-V centers. Strong absorptions from N-V centers are the main causes of the observed pinkish orange bodycolor.

Figure 2. Several defects were detected in the CVD synthetic diamond’s absorption spectrum in the UV-Vis-NIR region at liquid-nitrogen temperature. Strong absorptions from the N-V centers are the main cause of the observed pinkish orange color.
The very attractive orange color was achieved by introducing the proper concentrations of N-V centers while limiting the formation of other defects. It should be pointed out that the relatively high concentration of [Si-V]– could be attributed to the treatment by combining preexisting Si impurity with artificially introduced vacancies. With further developments in after-growth treatment, it is highly likely that more colors in CVD synthetic diamonds will be introduced. Source: GIA @topic:4


Title: Strain-Induced Birefringence in Natural Diamond: A Review Abstract: Diamond belongs to the cubic crystal system and should therefore exhibit isotropic optical properties. But it is well documented that diamonds often show weak birefringence. This study has focused on the causes of strain-induced birefringence in natural diamonds: dislocations, lattice parameter variations, inclusions, fractures, and plastic deformation.

Strain patterns shed light on the internal stresses within the stone, which in turn reveal the growth and transport history of the diamond. The imaging of diamonds between crossed polarizers remains a simple and rapid technique for obtaining visual information on strain patterns in diamonds.

Abstracted by Guy Lalous Source: GIA @topic:4


Title: Serenity Coated Colored Diamonds: Detection and Durability Abstract: Gemological, spectroscopic, and chemical properties of diamonds treated using the new Serenity Technologies coating technique for inducing various “fancy” colors are reported. This technique produces colors that include intense blue, green, yellow, and orange to pink to purple-pink. The presence of a coating can be identified with magnification by observation of an interference-related colored (often bronzy) film, scratches, and colorless and/or dark areas on the surface of the pavilion facets. UV-Vis absorption spectra and chemical analysis provide confirmation of the treatment. Chemical analysis also revealed that the coating is a SiO2 film doped with Au and/or Ag for blue, pink, and yellow coloration, or with a surface Fe2O3 film for orange. No evidence was detected of either chemical diffusion or implantation of foreign elements into the diamond. While the colors produced by this treatment are stable to some standard jewelry repair and cleaning procedures, they are not considered permanent. Source: GIA @topic:4


Title: Experimental CVD Synthetic Diamonds from LIMHP-CNRS, France Abstract: In the last decade, progress in diamond growth by chemical vapor deposition (CVD) has resulted in significant improvement in the quality of synthetic single crystals. This article reports on the gemological and spectroscopic features of six synthetic type IIa diamonds grown for research purposes at the French Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions (LIMHP-CNRS), and compares their diagnostic features to CVD-grown diamonds from other producers. Three of the six samples were nitrogen doped, whereas the other three were classified as high purity. A number of characteristics that are diagnostic of CVD synthetic diamond were present in the nitrogen-doped crystals, despite an absence of defect-related absorption features in the infrared region. Identification of the high-purity samples was more complicated, but it was still possible based on features in their photoluminescence spectra, their distinctive birefringence, and characteristic luminescence images. Source: GIA @topic:4


Title: An Updated Chart on the Characteristics of HPHT-Grown Synthetic Diamonds Abstract: A new chart, supplementing the one published in the Winter 1995 issue of Gems & Gemology, summarizes the features of both as-grown (“non-modified”) and treated (“modified”) synthetic diamonds currently in the gem market (that is, those grown by the high pressure/high  temperature technique). It includes photographs of visual features, information about visible-range absorption spectra, and illustrations of growth-structure patterns as revealed by ultraviolet fluorescence imaging. The chart is designed to help gemologists recognize the greater variety of laboratory-created diamonds that might be encountered today. Source: GIA @topic:4


Title: An Investigation into the Cause of Color in Natural Black Diamonds from Siberia Abstract: Black and dark gray diamonds from Siberia, Russia, were studied by analytical scanning and transmission electron microscopy. Their color is caused by the presence of dark inclusions. Unlike some previous reports on black diamonds in which the dark inclusions were primarily graphite, the Siberian samples with the most intense black color contained predominantly magnetite inclusions, while the dark gray diamonds most commonly contained inclusions of hematite and native iron. Moreover, the black diamonds studied exhibited anomalously high magnetic susceptibility, which may serve as one criterion for determining the natural origin of black color. Source: GIA @topic:4


Title: A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds Abstract: Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet radiation of a UV lamp. There is a perception in the trade that this fluorescence has a negative effect on the overall appearance of such a diamond. Visual observation experiments were conducted to study this relationship. Four sets of very similar round brilliant diamonds, covering the color range from colorless to faint yellow, were selected for the different commonly encountered strengths of blue fluorescence they represented. These diamonds were then observed by trained graders, trade professionals, and average observers in various stone positions and lighting environments. For the average observer, meant to represent the jewelry buying public, no systematic effects of fluorescence were detected. Even the experienced observers did not consistently agree on the effects of fluorescence from one stone to the next. In general, the results revealed that strongly blue fluorescent diamonds were perceived to have a better color appearance when viewed table-up, with no discernible trend table-down. Most observers saw no relationship between fluorescence and transparency. Source: GIA @topic:4


Title: Gemological Properties of Near-Colorless Synthetic Diamonds Abstract: Examination of 51 colorless to near-colorless synthetic diamonds from all known sources of production confirms that they can be distinguished from similar-appearing natural diamonds on the basis of their gemological properties. Although some may contain opaque metallic inclusions, the most distinctive feature of near-colorless synthetic diamonds is their luminescence to ultraviolet radiation and to an electron beam (cathodoluminescence). In particular, almost all fluoresce yellow or yellow-green to short-wave UV and, when the ultraviolet lamp is turned off, they continue to phosphoresce for 60 seconds or more. These distinctive reactions to ultraviolet radiation are very useful in identification, because many diamonds can be checked at one time. Source: GIA @topic:4


Title: Natural-Color Nonconductive Gray-to-Blue Diamonds Abstract: Two new categories of gray-to-blue diamonds are described. First, two type IIb blue crystals with what appears to be a type IIa outer skin were not electrically conductive in the rough, but conducted electricity once faceted. Second, some non-electrically conductive gray-to-grayish blue diamonds from the Argyle mine, Australia, were determined to be type Ia and to contain unusually high amounts of hydrogen. This latter type of coloration, not previously reported for diamonds, may be due to hydrogen-related defects in the crystal structure. Source: GIA @topic:4


Title: Recent Discoveries of Large Diamonds in Trinity County, California Abstract: Although California has produced over 600 diamonds, some of which have been of gem quality, the largest until recently weighed approximately 6 ct. In the early 1980s, however, Edgar J. Clark found a 3.90 ct stone; in 1987, he discovered three stones weighing 32.99, 17.83, and 14.33 ct. These four diamonds were recovered from stream gravels of Hayfork Creek in Trinity County, California. All four are of industrial grade and all have one interesting feature in common, that is, two generations of diamond growth. The initial crystal, or group of crystals, is encrusted by a later generation of diamond overgrowth that, although it conforms crystallographically to the underlying crystal, shows different crystal forms. This unusual feature, common to all four crystals, would indicate that they originated from the same source. Source: GIA @topic:4


Title: A Preliminary Gemological Study of Synthetic Diamond Thin Films Abstract: To evaluate possible problems in separating gem materials coated with a synthetic diamond thin film from their uncoated equivalents, we examined one sample of a free-standing, polycrystalline diamond film about one micron (0.001 mm) thick. This film could be easily recognized by standard microscopic examination, especially in surface-reflected and polarized light. The potential problems related to detecting thicker, monocrystolline, or colored synthetic diamond  thin films and coatings that might be encountered in the future on faceted stones are also briefly discussed. Source: GIA @topic:4


Title: Detection of Treatment in Two Unusual Green Diamonds Abstract: A pair of sharp absorption bands in the near-infrared region, referred to as H1b and H1c, have been detected in one (and the H1b band in the other) of two green diamonds known to have been treated. Until now these bands have been associated with the annealing of yellow to brown laboratory-irradiated diamonds. This is the first reported observation of these bands in green treated diamonds. Although these two diamonds may represent a special case, in that they are believed to have been irradiated, annealed, and then re-irradiated, the presence of one or both of these bands in a green diamond is one of the few reliable characteristics that identify that the stone has been treated in a laboratory. Source: GIA @topic:4


Title: The Changma Diamond District, Mengyin, Shandong Province, China Abstract: Since the early 1960s, Chinese geologists have conducted extensive exploration for diamonds. One of their most important discoveries to date is the Changma kimberlite district in Shandong Province, which encompasses two pipes and eight dikes. The most active mine currently, the Victory No. 1, produces approximately 6,000 ct of diamonds annually, 20% of which are gem quality. The ore is processed locally and the rough stones are given a preliminary sort before they are sent to special factories for cutting. Large, good-quality stones have been recovered at Changma; the largest to date weighs more than 119 ct. Source: GIA @topic:7


Title: Detecting HPHT Synthetic Diamond Using a Handheld Magnet Abstract: This study investigated the effectiveness of a handheld magnet in detecting synthetic diamonds. A total of 104 synthetic diamonds from nine different manufacturing sources were tested. Of the HPHT-grown synthetic samples tested, 58% registered a detectable magnetic response. Strong N52-grade neodymium magnets were able to detect 35% more HPHT synthetics than traditional ferrite and alnico magnets. CVD-grown synthetic diamonds showed no magnetic attraction. A set of 168 natural diamonds, including HPHT-treated natural diamonds, was tested as a control group. None of the natural transparent diamond samples showed attraction to a neodymium magnet, but two heavily included translucent specimens with unusually large opaque inclusions were strongly magnetic. A new magnetic testing method is presented for detecting small magnetic inclusions in loose HPHT-grown products, and for identifying small synthetic diamonds mounted in jewelry. Source: GIA @topic:4


Title: Characterization of a Synthetic Nano-Polycrystalline Diamond Gemstone Abstract: A potential new synthetic gem material in the form of a faceted 0.88 ct brownish yellow nano-polycrystalline diamond (NPD) has undergone a full gemological examination, including detailed spectroscopic analysis, for the first time. While the material’s implications for the gem industry are still unknown, NPD’s optical characteristics along with manufacturing improvements make it a potentially important synthetic for gemologists to be aware of, even though very few samples have been faceted and future production costs and availability for gem purposes are uncertain. Features seen with magnification may provide an indication of its nano-polycrystalline nature, and the identification of this material can be confirmed by spectroscopy and other advanced testing methods. NPD is an entirely new kind of synthetic diamond, and its development illustrates the ongoing research on diamond properties for a number of important applications beyond the field of gemology. Source: GIA @topic:4


Title: Nano-Polycrystalline Diamond Sphere: A Gemologist’s Perspective Abstract: Synthetic nano-polycrystalline diamond (NPD) is one of the latest and most exciting results of scientific efforts to synthesize a mineral that has held the fascination of humankind for ages. Unlike other forms of polycrystalline diamond, it is completely transparent. Owing to the material’s unique structure, it is also much tougher than natural diamond and previous synthetics, either single-crystal or polycrystalline. This represents a significant breakthrough for industrial purposes and for high-pressure research into the nature and properties of minerals, including diamond. Source: GIA @topic:4


Title: The Vallerano Diamond from Ancient Rome: A Scientific Study Abstract: Archaeological excavations during the 1990s at Vallerano, a municipality on Rome’s southern periphery, uncovered a cemetery from the Roman empire. One tomb was that of a young woman, believed to be of Syrian origin. It contained a wealth of everyday objects and jewels, among them a gold and diamond ring. The diamond’s gemological and spectroscopic properties were examined using portable instruments. Infrared spectroscopy indicated a type Ia diamond with evidence of B aggregates and probable A aggregates. Source: GIA @topic:1


Title: A Report on the New Watermeyer Split-Facet Diamond Cuts Abstract: Basil Watermeyer has introduced a new technique in diamond cutting that virtually eliminates the "bow-tie" effect commonly seen in the standard oval, marquise, and pendeloque cuts. It has also been adapted to the Barion emerald cut to provide even greater fountaining of light. The author describes these cuts and his experience with them using cubic zirconia. He also discusses their applicability to colored stones. Source: GIA @topic:4


Title: A History of Diamond Sources in Africa: Part II Abstract: Following the history of diamond discoveries in southern Africa presented in Part I, this article discusses the history of diamond exploration and mining in East and West Africa. The first economic kimberlite outside South Africa was discovered in Tanzania (East Africa) in 1940, and major quantities of large, high-quality alluvial diamonds have been mined in West Africa since the mid-1930s. Early miners struggled with misconceptions about how diamonds formed and concerns as to the depth to which diamonds could occur in pipes. Mining developments and new diamond occurrences in Africa led to many of the key concepts in modern diamond geology. Although Africa's long dominance in world diamond production has diminished in recent decades, its steady output and large reserves ensure its continuing role as the most important diamond-producing region in the world, surpassing in overall impact even Australia and Russia. Source: GIA @topic:7


Title: Diamond Sources and Production: Past, Present, and Future Abstract: Africa was the major source of diamonds for most of the 20th century, but Australia and Sakha (of the Russian Federation) now produce about half the world’s supply. Also, most of the production today comes from primary sources (kimberlites and lamproite), whereas secondary (alluvial) sources dominated as recently as the early 1970s. Although the annual production of rough more than doubled in the 1980s, the production of rough yielding good-quality polished gems has not increased appreciably. The economic potential of a kimberlite or lamproite occurrence depends on the tonnage and grade of the ore, as well as on the quality of the diamonds it contains. The authors predict that the early 21st century will see the Russian Federation as an even more important source of diamonds and Canada as a major producer. Source: GIA @topic:7


Title: Marine Mining of Diamonds off the West Coast of Southern Africa Abstract: A vast resource of gem-quality diamonds exists off the west coast of southern Africa. Over the course of millions of years, many diamond-bearing kimberlite pipes in the Orange River drainage basin have been extensively eroded and the released diamonds transported to the west coast. Raised marine deposits now on land have yielded almost 100 million carats of predominantly gem diamonds; similar marine deposits and feeder channels are now known to exist offshore. Techniques for exploiting the offshore resources have been proved on a small scale in shallow (<I5 m) waters. New technological developments in underwater mining systems have progressed to the point where mining has commenced in deep (about 100 m) Namibian waters. It is anticipated that production of diamonds from the sea will increase substantially in the future. Source: GIA @topic:7


Title: Characterization and Grading of Natural-Color Yellow Diamonds Abstract: To better understand the yellow diamonds currently in the marketplace, as well as identify possible changes in their trends seen over a five-year period, researchers at the GIA Gem Laboratory analyzed gemological data collected on more than 24,000 natural-color yellow diamonds examined in the calendar years 1998 and 2003. These data included color grade, type of cut, clarity grade, weight, ultraviolet fluorescence, and UV-visible and infrared spectra. Among natural-color colored diamonds, those with a yellow hue are some of the most abundant; even so, they are much less common than the colorless to light yellow diamonds associated with GIA’s D-to-Z color grading scale. Since the yellow color is a continuation of the gradation of color associated with the D-to-Z scale, there can be misconceptions about the color grading, which involves different procedures from those used for D-to-Z grading. The grading and appearance aspects, as well as other characteristics of yellow diamonds, are discussed to clarify these differences. The authors have also identified five subgroups of type I yellow diamonds, which (with some overlap) are characterized by representative spectra and color appearances. Source: GIA @topic:4


Title: X-Ray Fingerprinting Routine for Cut Diamonds Abstract: X-ray topography is a nondestructive technique that permits the visualization of internal defects in the crystal lattice of a gemstone, especially diamond, which is highly transparent to X-rays. This technique yields a unique “fingerprint” that is not altered by gem cutting or treatments such as irradiation and annealing. Although previously a complicated and time-consuming procedure, this article presents a simplified X-ray topographic routine to fingerprint faceted diamonds. Using the table facet as a point of reference, the sample is crystallographically oriented in a unique and reproducible way in front of the X-ray source so that only one topograph is necessary for fingerprinting. Should the diamond be retrieved after loss or theft, even after recutting or exposure to some forms of treatment, another topograph generated with the same routine could be used to confirm its identity unequivocally. Source: GIA @topic:4


Title: Characterization and Grading of Natural-Color Pink Diamonds Abstract: The GIA Gem Trade Laboratory (GTL) collected gemological data on 1,490 natural-color pink gem diamonds—both types I and II. While there was some overlap in gemological properties between the two diamond types, they did show differences in their color ranges, ultraviolet fluorescence, absorption spectra, and microscopic features. The color description terminology used for pink diamonds on GIA GTL grading reports is discussed and illustrated, with a separate commentary on red diamonds. Source: GIA @topic:4


Title: Star of the South: A Historic 128 Ct Diamond Abstract: The Star of the South is one of the world’s most famous diamonds. Discovered in 1853, it became the first Brazilian diamond to receive international acclaim. This article presents the first complete gemological characterization of this historic 128.48 ct diamond. The clarity grade was determined to be VS2 and the color grade, Fancy Light pinkish brown. Overall, the gemological and spectroscopic characteristics of this nominal type IIa diamond—including graining and strain patterns, UV-Vis-NIR and mid- to near-infrared absorption spectra, and Raman photoluminescence—are consistent with those of other natural type IIa diamonds of similar color. Source: GIA @topic:4


Title: Discovery and Mining of the Argyle Diamond Deposit, Australia Abstract: In 1983, the Argyle mine was established as the first major diamond-mining operation in Australia. Almost immediately, it became the world’s largest source of diamonds in terms of the volume (carats) produced. The discovery, development, and operation of this mine challenged conventional beliefs about diamond geology, mineral processing, and the marketing of gem diamonds. In its peak year, 1994, the mine produced over 42 million carats (Mct) of rough diamonds, which represented 40% of the world’s production. A large proportion of this staggering output consists of small brown-to-yellow—as well as some near-colorless and colorless—rough diamonds. A major cutting industry developed in India to process these diamonds into cut gems. The Argyle mine is also noted for the production of a very limited amount of rare pink diamonds. Source: GIA @topic:7


Title: Identification of HPHT-Treated Yellow to Green Diamonds Abstract: Examination of recently introduced greenish yellow to yellowish green HPHT-treated diamonds from three companies revealed several identifying characteristics. Gemological properties include a highly saturated body color, well-defined brown to yellow octahedral graining, moderate to strong green “transmission” luminescence to visible light (associated with the graining), and visual evidence of heating. Most of the treated diamonds, including some from each of the three sources, exhibit chalky greenish yellow to yellow-green fluorescence to UV radiation (long- and shortwave). Distinctive features seen with a handheld spectroscope include a 415 nm line, a strong band from about 480 to 500 nm, a strong line at 503 nm, and emission lines at 505 and 515 nm. IR spectra reveal that they are type Ia diamonds. Near-IR spectra show a peak at 985 nm, an indicator of high-temperature exposure. A small number of these HPHT-treated diamonds are yellow to brownish yellow; they do not show any green transmission, but other properties identify them as treated. Source: GIA @topic:4


Title: Fingerprinting of Two Diamonds Cut from the Same Rough Abstract: If it can be determined that two faceted diamonds came from the same piece of rough, romantic value is added to the stones. X-ray topography and cathodoluminescence (CL) tomography were used to prove that a round brilliant and a pear-shaped brilliant were cut from the same piece of rough. With these techniques, the internal imperfections and inhomogeneities that reflect the distinctive growth history of the original diamond crystal can be seen. X-ray topography is a powerful tool for imaging the distribution of lattice defects; CL tomography is more sensitive for detecting faint chemical inhomogeneities. By combining the two methods, the sophisticated gemologist can view both physical and chemical characteristics of a crystal, and thus its growth history, and use this information to fingerprint a given stone. Source: GIA @topic:4


Title: The Rise to Prominence of the Modern Diamond Cutting Industry in India Abstract: The modern diamond cutting industry in India began slowly in the late 1950s but did not gain momentum until the mid-1960s. In the 30 years from 1966 to 1996, the industry grew at a remarkable rate: 82-fold by polished weight and 249-fold by polished (wholesale) value. Today, India accounts for about 70% by weight and 35% by (wholesale) value of the diamonds polished annually worldwide (excluding the effects of recent temporary surpluses of Russian rough diamonds in the market), and it has a near-monopoly in smaller (less than 7 pt) stones. Using production, sales, and other statistics, this article reviews the rise of the modern diamond cutting industry in India and its impact on the world diamond trade. India has had a profound effect on this trade because of the enormous quantities of small, low-cost diamonds manufactured there. Source: GIA @topic:8


Title: Recent Advances in CVD Synthetic Diamond Quality Abstract: Synthetic diamond growth was first documented in 1952 by William Eversole of the Union Carbide Corporation, but it took another two decades before GIA issued the first grading report for a laboratory-made diamond (Crowningshield, 1971). Virtually all single-crystal synthetic diamonds are made by two very different processes. High-pressure, high-temperature (HPHT) synthesis mimics some of the key conditions for natural diamond formation, with pressures of 5–6 GPa and temperatures of 1400–1600ºC applied to a carbonaceous source material. The second method, chemical vapor deposition (CVD), involves growing synthetic diamond as thin-film layers at moderate temperatures and low (i.e., below atmospheric) pressures. One of the main advantages of the CVD procedure over HPHT is the superior flexibility of synthetic diamond size and geometry produced. Furthermore, intentional doping with impurity elements can be controlled by the addition of gases containing those atoms. Source: GIA @topic:4


Title: The “Type” Classification System of Diamonds and Its Importance in Gemology Abstract: Diamond “type” is a concept that is frequently mentioned in the gemological literature, but its relevance to the practicing gemologist is rarely discussed. Diamonds are broadly divided into two types (I and II) based on the presence or absence of nitrogen impurities, and further subdivided according to the arrangement of nitrogen atoms (isolated or aggregated) and the occurrence of boron impurities. Diamond type is directly related to color and the lattice defects that are modified by treatments to change color. Knowledge of type allows gemologists to better evaluate if a diamond might be treated or synthetic, and whether it should be sent to a laboratory for testing. Scientists determine type using expensive FTIR instruments, but many simple gemological tools (e.g., a microscope, spectroscope, UV lamp) can give strong indications of diamond type. Source: GIA @topic:4


Title: Boron Carbide: A New Imitation of Black Diamond Abstract: Figure 1. This 1.04 ct black submetallic round brilliant, initially represented as diamond, was identified as boron carbide. Photo by Gagan Choudhary.

              As black diamond has gained popularity in the past few years, so have aggregates of black synthetic moissanite and crystalline silicon (Spring 2011 Lab Notes, pp. 54–55). One specimen received by the Gem Testing Laboratory in Jaipur, a 1.04 ct black submetallic round brilliant (figure 1), appeared to be synthetic black moissanite but proved otherwise. The specimen was presented to the owner as a diamond.

	Figure 2. Under reflected light, the boron carbide specimen displayed a dense, fine granular structure typically associated with aggregates such as ceramics. Photomicrograph by Gagan Choudhary; magnified 48×.
Due to the prevalence of black synthetic moissanite in the marketplace and gem laboratories, we immediately checked for the typical aggregate structure under the microscope. Although a granular pattern was distinctly visible in reflected light (figure 2), it was much denser and finer than the kind usually seen in black synthetic moissanite. This raised uncertainty, so additional gemological tests were performed. The specimen had an over-the-limit RI, an SG of 2.43, and a hardness above 9 on the Mohs scale. The low SG value ruled out the possibility of synthetic moissanite (3.22), but otherwise offered no clues as to the specimen’s identity.

	Figure 3. The boron carbide’s Raman spectrum showed major peaks at approximately 260, 320, 480, 532, 720, and 1088 cm–1.
Qualitative EDXRF analysis revealed Fe, with traces of Si and K. Raman spectra taken from several points using 532 nm laser excitation showed major peaks at approximately 260, 320, 480, 532, 720, and 1088 cm–1, with smaller peaks at about 800, 824, 874, 967, and 998 cm–1 (figure 3). This combination of features did not match anything in our database, but an extensive literature search revealed an exact match with the Raman spectra of boron carbide (V. Domnich et al., “Boron carbide: Structure, properties, and stability under stress,” Journal of the American Ceramic Society, Vol. 94, No. 11, 2011, pp. 3605–3628, http://dx.doi.org/10.1111/j.1551-2916.2011.04865.x).

Boron carbide is an advanced ceramic material with high hardness, low density, thermal stability, and extreme abrasion resistance, making it suitable for nuclear, military, and aerospace applications. The material is typically produced by reacting and fusing carbon with boric oxide (B2O3) in an electric arc furnace, followed by a sintering process of hot pressing in graphite dies under a vacuum or argon atmosphere at temperatures of 1900–2200°C and pressures of 0.02–0.04 GPa for 15–45 minutes (Singhal and Singh, “Sintering of boron carbide under high pressures and temperatures,” Indian Journal of Engineering and Materials Sciences, Vol. 13, April 2006, pp. 129–134).

Although boron carbide is common in engineering and materials science—used as scratch-resistant coating and plating in tank armor, bulletproof vests, and padlocks—this was our first encounter with it as a diamond simulant. Our literature search (by Mr. Sandeep Vijay, a staff gemologist) did not reveal any gemological uses of this ceramic product. Distinguishing boron carbide from black diamond or synthetic moissanite was straightforward on the basis of SG, but Raman spectra and reference data were needed for identification. The possibility of market penetration cannot be ruled out. Source: GIA @topic:4


Title: Rapid Sight Estimates of Diamond Cutting Quality Abstract: A diamond brilliant’s beauty is the result of a complex combination of angles and proportions. In this article, Richard Liddicoat shows gemologists how to become familiar with how variations in cutting angles can affect a diamond’s face-up appearance. Using Marcel Tolkowsky’s ideal cut as a point of reference, Liddicoat presents techniques for estimating a particular diamond’s proportion values, describing how variables such as pavilion depth and size of table reflection influence the overall look and quality of a round brilliant. Source: GIA @topic:7


Title: Geo-Literary Society Explores Diamond Cut Abstract: At the February 2014 annual meeting of the Geo-Literary Society in Tucson, speakers Al Gilbertson (left) and Scott Sucher (right) discussed the evolution of diamond cutting.

                      The Geo-Literary Society held its annual meeting on Friday, Feb. 14 at the Tucson Convention Center. The event, which drew attendees from the Tucson Gem and Mineral Shows, featured presentations by Scott Sucher and Al Gilbertson in a session titled “The Evolution of Diamond Cutting.”

Sucher, president of The Stonecutter in Albuquerque, New Mexico, has created replicas of famous diamonds for more than 30 years. Gilbertson, a research associate at GIA in Carlsbad, California, has authored numerous articles on diamond cut and grading, as well as the 2007 book American Cut: The First 100 Years.

Sucher opened the session by chronicling the early history of diamond use, global trade patterns, and advances in cutting techniques and styles (see table). Using computer models, he compared the brilliance and fire of several early diamond cuts.

Table: Milestones in the early history of diamonds and diamond cutting

				ca. 1000 BC

				First archeological evidence of diamond as a cutting tool

				ca. 300 BC

				Early Indian manuscript discusses the qualities of diamond

				50 AD

				Pliny’s description of diamond use in engraving and jewelry

				1200s

				Development of the point cut (an octahedral crystal with polished faces); arrival of Indian diamonds in Europe’s royal inventories

				Early 1300s

				Establishment of cutting centers in Antwerp, Venice, and Amsterdam

				Mid 1300s

				Development of the table cut, a point cut with its top portion cut off to create a table-like surface

				Late 1300s

				Development of the single cut, a table cut with additional facets on the corners

				1400s

				Advent of the polishing wheel (scaife), and the discovery of cleaving as a faster way of shaping diamond

				1500s

				Improvements to the scaife, allowing polishing speeds of 1000 rpm

				1600s

				Development of the Mazarin, a double-cut brilliant

				1700s

				Development of the Old Mine cut, and the cutting of the famous Wittelsbach (prior to 1664) and French Blue (1671–1673) diamonds

Gilbertson picked up the story with the discovery of Brazilian diamond deposits around 1725, which ushered in a period of glittery excess among European elites. David Jeffries, whose 1750 treatise described the use of a handheld “prover” to measure cutting angles, coined the term “round brilliant” for a cut that contained 58 facets.

The discovery of massive diamond deposits in South Africa in 1867 changed the course of the industry, making these treasures available to a mass market. By 1870, there were 10,000 cutters in Europe. These artisans followed the shape of the original crystal and kept as much of the original weight as possible.

But the emphasis on weight retention was beginning to unravel thanks to Henry Morse, who had set up a cutting shop in Boston around 1860. Morse, who once said, “Shopping for diamonds by the carat is like buying a racehorse by the pound,” emphasized the cut of a stone and the brilliance that resulted. He invented a gauge to measure crown and pavilion angles, and devised his own set of best proportions. He also helped develop mechanical bruting, which increased the production of round-cut diamonds.

With turn-of-the-century improvements such as the circular saw, which made it easy to cut two diamonds from a rough crystal, the stage was set for the modern round brilliant. In 1919, Belgian engineer Marcel Tolkowsky published a landmark book titled Diamond Design, in which he asserted that the best-cut stones feature a 53% table, 59% total depth, and a knife-edged girdle. With some modifications to Tolkowsky’s proportions—an extended lower half, a larger table, and a closed-up culet—the round brilliant as we know it was established by 1950.

As Gilbertson pointed out, the breakthroughs in diamond cut planning and evaluation were just beginning. The Firescope viewer, developed in 1986, allowed the user to see a “Hearts and Arrows” pattern in a diamond cut to these “ideal” proportions. The Sarin scanner, introduced six years later, offered rapid, accurate proportion measurement, which led to the various cut grading services available today. Among other recent advances are inclusion-mapping software and high-speed laser cutting.

Following the presentation, Sucher invited the audience to view his faceted replicas of Cullinans I and II, the Koh-i-Noor, the Hope, and several other historical diamonds.

“Scott Sucher transported us to the early days of diamond cutting as we learned the first sources and tools,” said Dona Dirlam, the Geo-Literary Society’s secretary and the host of the session. “We saw how cutting styles evolved with improvements in the tools and an increase in the diamond supply. With each development, we saw this fascinating transformation through visual models.

“Al Gilbertson told us the largely unknown story of Henry Morse and chronicled the birth of the modern round brilliant,” Dirlam added. “As Al and Scott pointed out, today’s computer-optimized diamond cutting seems light-years removed from the earliest techniques.” Source: GIA @topic:7


Title: Silicon in Natural Type IIa and Type IaB Diamond Abstract: The presence of Si in diamond is typically revealed by detection of the 736.6/736.9 nm (“737 nm”) doublet zero-phonon line (ZPL), observed by either absorption or photoluminescence (PL) spectroscopy. This feature has been assigned to the negatively charged state of the silicon split-vacancy defect, SiV–, which is frequently incorporated into CVD synthetic diamonds due to the etching of silicon-containing growth chamber components. Conversely, reports of the 737 nm peak in natural or HPHT synthetic diamonds are notably rare (see C.M. Breeding and W. Wang, “Occurrence of the Si-V defect center in natural colorless gem diamonds,” Diamond and Related Materials, Vol. 17, 2008, pp. 1335–1344; Winter 2010 Lab Notes, p. 302; Winter 2012 Lab Notes, pp. 304–305). Consequently, this feature is considered an important tool for identifying CVD synthetic diamonds.

Recently, SiV– was detected in the PL spectra (liquid-nitrogen temperature with 633 nm laser excitation) of five diamonds submitted to GIA’s Mumbai laboratory. These 0.31–0.90 ct round brilliants were issued colorless grades of either D or E. Their clarity grades ranged from VVS1 to SI2, where the lower grades arose from the presence of trapped crystalline inclusions.

FTIR spectroscopy revealed that four of the samples were type Ia, with hydrogen-related peaks at 3107 and 1405 cm–1. The remaining sample was type IIa, with no discernible impurity-related IR features. Multi-laser, liquid-nitrogen-cooled PL spectra acquired for the fifth sample were similar to those reported in Breeding and Wang’s 2008 investigation of SiV– in natural diamonds. The latter also showed
luminescence at 737, 714.6, 589.8, 557.8/558.2, 554.2, and 550.3 nm, in addition to NV0/– (575 and 637 nm, respectively) and 3H (503.4 nm). This SI2 sample contained several inclusions with intact crystalline faces, identified by Raman spectroscopy as olivine, consistent with the former investigation (figure 1, top). Through gemological and spectroscopic observations, it was possible to distinguish this natural type IIa diamond from Si-containing type IIa CVD synthetics.

	Figure 1. Room-temperature Raman spectroscopy (830 nm laser excitation) identified the different inclusions in the type IIa, SI2 (top) and type IaB, SI1 (bottom) natural diamonds containing silicon. The former spectrum is consistent with olivine, while the latter is attributed to spessartine garnet.

The type Ia diamonds studied by Breeding and Wang all contained A-aggregates and varying concentrations of B-aggregates (type IaA±B). In the present group of type Ia diamonds, only B-aggregates were detected (pure type IaB). With the exception of the 737 nm feature, the type IaB diamonds’ PL spectra did not include any of the spectroscopic features characteristic of Si-containing type IaA±B diamonds. An emission line at 664.3 nm was detected in all the type IaB specimens, however. These samples also showed emissions from NV0/– (575 and 637 nm, respectively), H3 (503.2 nm), and H4 (495.9 nm), where H4 was remarkably strong for three of the diamonds. Interestingly, the diamond with the lowest H4 concentration was also distinctly included (SI1 clarity). Raman spectroscopy identified the inclusions as spessartine garnet (figure 1, bottom). Breeding and Wang also reported the presence of garnet in Si-containing diamonds. The presence of olivine and garnet inclusions in natural diamonds containing SiV– has been suggested to indicate that they crystallized in an area of mixed-composition peridotite in the upper mantle.

These results emphasize that the detection of SiV– in diamonds does not unequivocally signify CVD synthetic origin. Nevertheless, careful analysis of spectroscopic features and crystalline inclusions can be used to separate these natural diamonds and their synthetic counterparts. Source: GIA @topic:4


Title: CVD-Grown Synthetic Diamonds, Part 3: Detection Abstract: This Gemesis CVD synthetic diamond shows green fluorescence to the short-wave UV radiation of the DiamondView instrument. Image by Wuyi Wang.

Part 1 of this series provided a brief history of CVD synthetic diamonds, while part 2 examined their properties.

The CVD (chemical vapor deposition) process produces gem-quality synthetic diamond of great beauty, with properties virtually identical to those of natural diamond. Because of their high purity, these CVD products are type IIa—as are only a small percentage of natural diamonds. Therefore, any type IIa diamond should be sent to a well-qualified testing laboratory for identification. Detection has advanced to the point where any CVD-grown sample can be identified with certainty.
The CVD growth process itself occurs under conditions that bring about readily detectable features, including:

1. a low-pressure, highly energetic hydrogen-rich environment
2. the presence of silicon from grower parts
3. the presence of residual nitrogen in the grower
4. the layer-by-layer addition of carbon atoms on the growing surface

The hydrogen-rich environment leads to defects known as vacancies, in which occasional carbon atoms are missing from their proper location in the diamond crystal. A carbon vacancy residing next to a silicon atom can form a silicon-vacancy (Si-V) center, which is extremely rare in nature. A carbon vacancy next to a nitrogen atom may form a nitrogen-vacancy (N-V) center, which is rarely found in nature. These two vacancy-related defects are detectable through spectroscopic measurements such as photoluminescence, ultraviolet illumination, and optical absorption. In the case of the layer-by-layer growth feature, nitrogen is non-uniformly incorporated into the layers, causing growth striations visible under a DTC DiamondView.

	The DiamondView ultraviolet imaging system allows the operator to see a sample's fluorescence patterns from different directions. These patterns are useful in identifying CVD synthesis. Photo by Kevin Schumacher.
Pink-colored CVD synthetics are also readily detected by their abundance of N-V centers. Blue CVDs have been produced by adding boron to the growth chamber, though boron can slow growth so much that only thin films are produced. But even those thin films exhibit CVD-grown features.

In summary, CVDs are readily detected in a gem lab, in specimens of any size or color. Detectable features can change under heat treatment (at low or high pressure), but these changes are well understood and can still provide unambiguous detection of CVD-grown synthetic diamonds. For a detailed scientific study and extensive bibliography of detection, see W. Wang et al, “CVD Synthetic Diamonds from Gemesis Corp.,” Summer 2012 Gems & Gemology, pp. 80–97. Source: GIA @topic:4


Title: Infrared Microspectroscopy of Natural Argyle Pink Diamond Abstract: One of the most distinctive characteristics of natural pink diamond is the lamellae, or “graining,” in which the color resides. These features are believed to have formed under plastic deformation. A great deal of research has focused on color centers in diamond, particularly the N-V center. This article investigates the crystalline defect responsible for pink coloration in natural diamond. Infrared microspectroscopic images were obtained to estimate the spatial distribution of B-centers in natural pink Argyle diamonds. The spatial distribution of the nitrogen B-center (N–V–N3) was anti-correlated with the intensity of pink coloration. The authors believe this is the first such observation. IR spectral features were not influenced by exposure to UV illumination, in contrast to the visible change in coloration under the influence of UV radiation.

Abstracted by Guy Lalous Source: GIA @topic:4


Title: Strain-Induced Birefringence in Natural Diamond: A Review Abstract: Diamond belongs to the cubic crystal system and should therefore exhibit isotropic optical properties. However, it has long been documented that diamonds often show weak birefringence. This study has focused on the causes of strain-induced birefringence in natural diamonds. Dislocations, lattice parameter variations, inclusions, fractures and plastic deformation are the causes of strain-induced birefringence in diamonds.

Strain patterns shed light on the internal stresses within the stone, which in turn give indications as to the growth and transport history of the diamond. The imaging of diamonds between crossed polarizers still remains a simple and rapid technique for obtaining visual information on strain patterns in diamonds.

Abstracted by Guy Lalous Source: GIA @topic:4


Title: Boron Carbide: A New Imitation Black Diamond Abstract: Figure 1. This 1.04 ct black submetallic round brilliant, initially represented as diamond, was identified as boron carbide. Photo by G. Choudhary.

                      As black diamond has gained popularity in the past few years, so have aggregates of black synthetic moissanite and crystalline silicon (Spring 2011 Lab Notes, pp. 54–55). One specimen received by the Gem Testing Laboratory in Jaipur, a 1.04 ct black submetallic round brilliant (figure 1), appeared to be synthetic black moissanite but proved otherwise. The specimen was presented to the owner as a diamond.

Due to the prevalence of black synthetic moissanite in the marketplace and laboratories, we immediately checked for the typical aggregate structure under the microscope. Although a granular pattern was distinctly visible in reflected light (figure 2), it was much denser and finer than the kind usually seen in black synthetic moissanite. This raised uncertainty, so additional gemological tests were performed. The specimen had an over-the-limit RI, an SG of 2.43, and a hardness above 9 on the Mohs scale. The low SG value ruled out the possibility of synthetic moissanite (3.22), but otherwise offered no clues as to the specimen’s identity.

	Figure 2. Under reflected light, the boron carbide specimen displayed a dense fine granular structure typically associated with aggregates such as ceramics. Photomicrograph by G. Choudhary; magnified 48x.
Qualitative EDXRF analysis revealed Fe with traces of Si and K. Raman spectra taken from several points using 532 nm laser excitation showed major peaks at approximately 260, 320, 480, 532, 720, and 1088 cm-1, with smaller peaks at about 800,824, 874, 967, and 998 cm-1. This combination of features did not match anything in our database, but an extensive literature search revealed an exact match with the Raman spectra of boron carbide (V. Domnich et al., “Boron carbide: Structure, properties, and stability under stress,” Journal of the American Ceramic Society, Vol. 94, No. 11, 2011, pp. 3605–3628).

Boron carbide is an advanced ceramic material with high hardness, low density, thermal stability, and extreme abrasive resistance, making it suitable for nuclear, military, and aerospace applications. The material is typically produced by reacting and fusing carbon with boric oxide (B2O3) in an electric arc furnace, followed by a sintering process of hot pressing in graphite dies under a vacuum or argon atmosphere at temperatures of 1900–2200oC and pressures of 0.02–0.04 GPa for 15–45 minutes (Singhal and Singh, “Sintering of boron carbide under high pressures and temperatures,” Indian Journal of Engineering and Materials Sciences, Vol. 13, April 2006, pp. 129–134).

Although boron carbide is common in engineering and materials science—uses such as scratch-resistant coating and plating in tank armor, bulletproof vests, and padlocks—this was our first encounter with it as a diamond simulant. Research also did not reveal any gemological uses of this ceramic product. Distinguishing boron carbide from black diamond or synthetic moissanite was straightforward based on SG, but Raman spectra and reference data were needed for identification. The possibility of market penetration cannot be ruled out.

Acknowledgment: Mr. Sandeep Vijay, staff gemologist at the Gem Testing Laboratory, for conducting a thorough literature search. Source: GIA @topic:4


Title: Large Pinkish Brown CVD Synthetic Diamond Abstract: Figure 1. This 1.03 ct CVD synthetic is notable for its size and Faint pinkish brown color. Photo by Robison McMurtry.

              Distinguishing diamonds of natural and synthetic origin is one of the most important tasks of any gemological laboratory. With the advances in technology and methodology available to manufacturers, a wider variety of synthetic diamonds has begun to emerge. Recently, a client submitted a 1.03 ct emerald-cut synthetic diamond (figure 1) to the Carlsbad laboratory. We determined it had been grown from the chemical vapor deposition (CVD) process. This was evident from the large silicon-vacancy peak at 737 nm seen in both the UV-visible and photoluminescence spectra of this type IIa synthetic diamond. A lack of tatami strain and the distinctive growth patterns observed in the DiamondView (see W. Wang et al., “Latest-generation CVD-grown synthetic diamonds from Apollo Diamond Inc.” Winter 2007 G&G, pp. 294–312) confirmed the origin (figures 2 and 3).

	Figure 2. Viewed under crossed polarizers, this synthetic diamond shows mottled strain, but no tatami strain, consistent with its CVD growth origin. Photo by Troy Ardon.

	Figure 3. DiamondView imaging remains one of the most reliable methods for confirming a CVD synthetic diamond. This image shows distinctive growth patterns. Image by Sally Eaton-Magaña.
As the vast majority of CVD synthetic diamonds submitted to the lab weigh less than one carat, this sample was unusual for its size, as well as its color grade of Faint pinkish brown. This is the first colored CVD synthetic diamond examined by GIA that did not merit a “Fancy” modifier, but instead fell in the Faint to Light range. While pink CVD-grown synthetics have been documented, in most cases the color was generated by post-growth treatment. Here the pinkish color seemed solely related to the growth process, with no subsequent treatments (HPHT annealing, irradiation, and then annealing) coming into play. Source: GIA @topic:4


Title: A 118.28 ct Diamond Achieves Record Price Abstract: Patti Wong, chairman of Sotheby’s Asia and Sotheby’s Diamonds, holds a 118.28 ct D-Flawless stone that became the most expensive colorless diamond ever sold at auction.

                      On Oct. 7, a 118.28 ct D-Flawless diamond broke a world record when it sold for $30.06 million at Sotheby's Magnificent Jewels & Jadeite auction in Hong Kong.

The oval-cut had garnered a price estimate of $28 to $35 million. Another anticipated record-breaker, a 7.59 ct Fancy Vivid blue Internally Flawless diamond, fell $3 million short of its estimated $19 million sale price. An Internally Flawless round brilliant, the gem's cut is rare for a fancy-color diamond, as it's designed to maximize brilliance and minimize color.

The colorless—which ranks as the largest oval-cut D-flawless GIA has ever graded—was mined in southern Africa about two years ago and cut from a 299 ct rough. Because it is newly cut, said Patti Wong, chairman of Sotheby’s Asia and Sotheby’s Diamonds, the buyer has the opportunity to name it.

It’s not just the size of this diamond that makes it exceptional. The pre-sale price estimate was made public, said Wong, a contrast from the usual auction practice of noting “estimate upon request” for major stones.

	On Oct. 7, the 118.28 ct diamond sold for $30.06 million at Sotheby's Magnificent Jewels & Jadeite auction in Hong Kong. Photo courtesy of Sotheby's.
“I believe that if you have something good, flaunt it,” she said before the auction, adding that the estimate was “very defensible in light of prices realized [for very large colorless diamonds] during the previous four auctions.” In May, the 101.75 ct D-Flawless Winston Legacy sold for $26.7 million at Christie’s Geneva.

Wong said that auctioning the diamond in Hong Kong instead of Geneva or New York reflected a natural evolution of the market.

“All of the previous hundred-carat D-Flawless [and Internally Flawless] sold at auctions have been in Geneva,” she said. “But in the past five years, many of the record prices have been set at Hong Kong sales.” She cited the 6.01 ct Fancy Vivid blue that achieved the highest-ever per-carat price for a blue diamond ($1.686 million) in 2011 and the 5 ct Vivid Pink that shattered the per-carat price record for any diamond ($2.16 million) in 2009.

	The oval-cut diamond was fashioned from this 299 ct rough found in southern Africa
	in 2011. Photo courtesy of Sotheby's.

The fast growth of Asian economies is a key reason Hong Kong has become one of the world’s top auction venues, with dealers from around the world flocking there to buy and sell.

“Ten years ago, Asian private buyers bought almost everything at the sales here,” Wong said. “These buyers, and the previews of major pieces offered at other locations, helped the auction houses establish a solid base here. Now all the world’s top dealers are coming here, which is why records are being set.” Source: GIA @topic:8


Title: Synthetic Diamonds: Improved Quality and Identification Challenges Abstract: CVD synthetic diamonds produced by Gemesis. The 0.39 ct. round brilliant on the left was graded F color and VVS2 clarity; the 0.83 ct. sample on the right was graded J color and VVS2 clarity. Image © GIA.

                      Colorless synthetic diamonds produced by Chemical Vapor Deposition (CVD) are becoming more common in the market. CVD-processed stones are much different from the natural diamonds produced by geologic forces. They are also vastly different from the High Pressure, High Temperature (HPHT) synthetics that have been manufactured since the mid-1950s.

CVD synthetic diamonds began appearing in the gem diamond market about a decade ago. The process involves introducing a gas, such as methane, into a vacuum chamber, then activating and breaking down the molecules of the gas with microwaves. This causes the carbon atoms to accumulate on a substrate (a small platform containing a flat diamond seed crystal, usually an HPHT synthetic), similar to the way snowflakes accumulate in a snowfall.

The HPHT method, first used to successfully grow diamonds by General Electric in 1954, essentially mimics the natural process - carbon is crystallized as diamond through intense heat and pressure deep within the Earth. The HPHT process is very costly, given the energy and equipment required, and produces diamonds with mainly yellowish or brownish yellow colors.

The CVD method is much less costly because it works at moderate temperatures and low pressure, which requires smaller and less expensive equipment. Because the vacuum chamber contains only carbon and some hydrogen, colorless crystals can be grown. If nitrogen or boron is introduced into the chamber, yellow or blue synthetic diamond crystals can be produced.

At first, the creators of these CVD diamonds thought they would be able to produce diamonds quickly and cheaply. However, because the quality was inconsistent and the typical brown colors were less than desirable, those expectations were not met.

In the past decade, CVD producers have found that changing the gases in the growth chamber and using a purer Type II synthetic diamond as a seed crystal can improve the color of the finished synthetic diamond and speed the growth rates. Since many early CVDs had a brownish color, producers also found that treating the material at high temperatures and pressures can remove the brown coloration to make the crystals colorless. This treatment step masked some of the signature features, which resulted in the identification of these synthetic diamonds becoming more difficult.

The Gemesis Corporation of Sarasota, Florida, which produced its earlier synthetic diamonds with the HPHT-process, began to market colorless CVD synthetic diamonds in March 2012. There are several other companies which also sell CVDs.

GIA researchers purchased 16 CVD diamonds from Gemesis, 15 of them cut into round brilliants, ranging from 0.24 carats to 0.86 carats. The majority had very high colors, ranging F-G on the GIA 4Cs scale. Three were I-J. The largest, at 0.90 carats, was a rectangle cut graded L, since it showed a slight yellowish cast.

The researchers, led by Dr. Wuyi Wang, GIA’s director of research and development, subjected these synthetic diamonds to an extensive battery of tests. The tests included several sophisticated types of spectral analysis to obtain a telltale “signature” of samples created by the CVD process. By using advanced instrumentation, scientists can read the diamonds’ spectral signature to determine their composition, or whether they originated in nature or a laboratory. The GIA researchers also conducted standard gemological tests, including checking for features known to be diagnostic for other synthetic diamonds, such as graining patterns and ultraviolet fluorescence reactions. Diamonds have a grain, like wood, that is a result of the way they crystallize, but because they grow differently in nature than in a lab, the grain patterns of synthetic diamonds are different.

The GIA tests found that the quality of colorless to near-colorless CVD-grown diamonds has improved significantly in the decade since they were introduced. In the past, CVD synthetics displayed graining patterns not found in natural diamonds, as well as distinctive fluorescence reactions. These samples showed that separating such stones from natural diamonds requires the use of advanced spectroscopic techniques. In addition, it was apparent that the synthetics were treated under high heat to remove or obscure some of their telltale features, such as graining which, after treatment, is very difficult to see.

Despite the difficulty in spotting these stones by conventional means, GIA researchers did find unique spectroscopic signatures. They did so by subjecting photoluminescence and ultraviolet fluorescence reactions to the DiamondView™, a sophisticated instrument used by gemological labs to detect synthetic diamonds.

GIA continues to make synthetic diamonds a top research priority so it can identify and report on the latest developments of these lab-created stones. Source: GIA @topic:4


Title: CVD-Grown Synthetic Diamonds, Part 2: Properties Abstract: These CVD synthetic diamonds produced by Gemesis Corp. range in size from 0.24 to 0.90 ct. Photo by Robert Weldon

Part 1 of this series provided a brief history of CVD synthetic diamonds.

The physical properties of CVD synthetic diamond fall well within the range for natural diamonds in terms of hardness, thermal conductivity, strength, and so forth. Therefore, CVD synthetics are as hard and durable as natural diamond and display the same brilliance and fire when cut as a gemstone. The optical properties can be varied over a wide range through the controlled introduction of impurities. For example, crystals can be made colorless to near-colorless by controlling the residual nitrogen level of the gas in the growth chamber. Blue diamonds can be created by adding boron to the gas, while pink, yellow, or other variations can be achieved using mixtures of gases, including high nitrogen concentrations. One particular advantage of CVD diamond production is that all crystals in a growth batch have the same color and clarity, making them easier to grade and match. And the color can be accurately repeated over an endless number of growth runs, ensuring reproducible color, clarity, and size, and an ongoing supply of high-quality synthetic diamonds for the gem industry. In addition, the ability to control size and purity will expand the uses of synthetic diamond beyond what is possible with natural diamonds, into new areas in optics, medical devices, electronics, and applications yet to be identified.

Other Properties
Colorless and near-colorless CVD synthetic diamonds are usually type IIa, while only 2% of natural gem diamonds are type IIa. Type IIa diamonds are characterized by high purity (low nitrogen) and transparency in specific parts of the ultraviolet and infrared optical spectrum. Numerous UV detection instruments on the market can provide the first indication of a possible CVD synthetic. Obviously, additional tests would then be required to confirm whether the sample is CVD-grown or natural. If the gem is not IIa, it is most certainly natural. There will be additional discussion about non-IIa synthetic diamonds and the properties of blue, pink, yellow, and other colors in a future article.

A common question in the diamond trade and among consumers is whether CVD synthetics will eventually be manufactured so inexpensively that the value of natural diamonds endangered. The answer to that question is no. While CVD growth will become more efficient due to scale and manufacturing experience, several factors will only become more expensive with time and inflation. First, the cost of cutting and polishing CVD products is essentially the same as for natural diamond, and highly skilled artisans will still be needed to create beautiful goods. A second factor is that the electricity required to produce one carat of diamond does not scale significantly with the number of seeds or chamber size. Electricity is a major cost, one that is expected to continue rising in the future, and there is little room for cost reduction here. A third cost is that of producing seeds. This is a significant overhead, and it is unlikely that an inexpensive alternative for a diamond seed will ever be found.

A more persistent threat to integrity and pricing in the diamond industry will be the misrepresentation of cubic zirconia and other imitation materials as “synthetic diamond.” While there are adequate tests for these imitations, they are not readily available for purchases made on the web.

Conclusions
CVD synthetics can be grown in a range of colors and sizes, with high clarity. The gemstones produced are as beautiful and durable as natural diamond, and they are expected to fill an important market niche in the near future. It is important to note that GIA has the ability to detect and grade CVD synthetics, which will continue to protect buyers and the integrity of the diamond industry.

In the next installment of this series, we will discuss detection of CVD synthetic diamonds. Source: GIA @topic:4


Title: CVD-Grown Synthetic Diamonds, Part 1: History Abstract: Dating back to the 19th century, there have been many claims for creating diamond in a lab. For many years, the conventional wisdom was that diamond would form only under conditions of high pressure and high temperature (HPHT). Indeed, the first commercially available “manmade” diamond was produced at high pressure and high temperature by General Electric in 1956. HPHT growth imitates natural diamond formation, but with carefully selected input materials to catalyze crystal growth. Today, billions of carats of diamonds are manufactured annually by the HPHT process, mostly for industrial applications.

In 1954, two years before the announcement of HPHT synthesis, a patent was issued for another type of diamond growth: the CVD (chemical vapor deposition) process. Early reports of gem-quality CVD synthetic diamond were greeted with skepticism and not verified until many years later. In the late 1980s, scientists with a highly advanced understanding of the technique discovered how to reproducibly grow diamond using the CVD process.

The CVD process is quite different from natural diamond formation. It produces diamond from a heated mixture of a hydrocarbon gas (typically methane) and hydrogen in a vacuum chamber at very low pressures. Under normal circumstances, heating this mixture at such low pressures would produce graphite or some other non-diamond form of carbon. But in a CVD growth chamber, some of the hydrogen is converted to atomic hydrogen, which promotes diamond formation since diamond is more stable in this environment. The conversion of molecular hydrogen to atomic hydrogen is accomplished through methods such as the application of microwave energy, an electric discharge, or hot filaments. When atomic hydrogen is present in the gas phase, two chemical processes occur:

(1) Graphite and other non-diamond carbon react with the atomic hydrogen and evaporate in a newly formed gas phase.
(2) Atomic hydrogen reacts with the original hydrocarbon gas (methane) to form a highly reactive carbon-hydrogen species. When this species decomposes, it gives up its hydrogen to form pure carbon: diamond.

To produce a gem-quality synthetic diamond, a diamond seed crystal (natural, HPHT, or CVD in origin) is introduced into the gas mixture, at an elevated temperature of 900 to 1200°C. The activated carbon-hydrogen species travels across the surface of the diamond seed until it finds an available carbon atom, and then attaches itself to this seed atom. The seeded growth is now one carbon atom thicker. This process repeats itself endlessly to replicate the crystal structure of the diamond seed crystal in three dimensions.

	Figure 1. This photo shows the growth of colorless diamond, approximately 1 mm thick, on a yellow HPHT-grown diamond seed.
Figure 1 shows the growth of colorless diamond on a yellow HPHT-grown diamond seed. This particular crystal is approximately 1 mm thick. Thicker crystals can be produced by extending the growth time, either by leaving the crystal in the growth chamber or by removing the seed, inspecting it, and returning it to the chamber for additional growth. To date, diamond crystals 3 to 5 mm thick have been grown and fabricated into gemstones. One of the subtleties of seeded CVD growth is that even though it can produce thick growth vertically, lateral growth is limited by quality considerations. Thus the seed diameter must be at least as large as the desired diameter of the final gemstone. Each new gem growth requires a seed crystal, so either the seed must be reclaimed and reused, or growth capacity must be set aside to continuously manufacture seeds.

The earliest CVD growth chambers enabled growth on only one seed at a time. Although reactor seed capacity is a closely guarded industrial secret, some CVD manufacturing systems are reportedly capable of growing on 50 or more seeds simultaneously. That number is expected to increase in the future.

	Figure 2. CVD-grown cut and polished synthetic diamonds.
CVD synthetics are cut and polished in the same manner as natural diamonds, at the same cost. The stones can be laser inscribed on the girdle to allow easy preliminary identification. Figure 2 shows typical CVD-grown cut and polished synthetic diamonds.

In the next installment of this series, we will look at the properties of CVD synthetic diamonds. Source: GIA @topic:4