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October 28, 2008

High Quality Kilocarat Diamonds


Carnegie Institution in Washington, D.C., has improved their diamond making process to enable thousand carat diamonds and larger. The largest cut diamond is 545.67 carats.

The Carnegie team could take these synthetic diamonds and anneal them at temperatures up to 3,632 degrees Fahrenheit (2,000 degrees Celsius) at pressures below atmospheric pressure. The annealing process turns the diamond crystals, which are originally yellow-brown, colorless or light pink.


Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell Hemley of the Carnegie Institution’s Geophysical Laboratory used a method called chemical vapor deposition (CVD) to grow synthetic diamonds for their experiments. Unlike other methods, which mimic the high pressures deep within the earth where natural diamonds are formed, the CVD method produces single-crystal diamonds at low pressure. The resulting diamonds, which can be grown very rapidly, have precisely controlled compositions and comparatively few defects.

The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality” says coauthor Ho-kwang Mao. Because the method does not require a high pressure press, it promises faster processing of diamonds and more types of diamonds to be de-colored than current high-pressure annealing methods. There is also no restriction on the size of crystals or the number of crystals, because the method is not limited by the chamber size of a high pressure press. The microwave unit is also significantly less expensive than a large high-pressure apparatus.


Color, Cut, Clarity and Carat
Synthetic-diamond makers received a boost in January, 2007 when the Gemological Institute of America--the organization that invented the color, cut, clarity and carat diamond standards 50 years ago--began grading the quality of lab-grown diamonds.

It takes Gemesis four days to grow a diamond of an average 2.5 carats. It uses about 20 kilowatt-hours per carat. Most cultivated (synthetic) diamonds come in colors, the natural counterparts of which are rare in nature and pricey in stores. Gemesis specializes in yellow diamonds that get their tint from a boost in nitrogen. Gemesis' Lux estimates the potential market for yellow diamonds alone to be in the tens of millions of dollars. He hopes to create more colorful and larger gems over the next five years. Apollo Diamond produces colorless stones from a quarter carat to a half carat in size.

Mined and synthetic diamonds are chemically identical. Neither the naked eye, nor an ordinary microscope can detect the difference. Jewelers can tell with a loupe [ten times magnification] by reading a laser inscription required by the Federal Trade Commission. [the diamond industry had laws passed that required laser etching of diamonds to label them synthetic or mined.] Otherwise, it takes high-tech equipment that analyzes the crystal structure of diamonds (like a proprietary machine De Beers has) to distinguish the difference.

While a natural, one-carat amber-colored diamond might retail for $20,000 or more, the Florida-based manufacturer Gemesis sells a one-carat stone for about $6,000. But no one, Gemesis included, wants to sell diamonds too cheaply lest the market for them collapse.

Apollo can create completely colorless and flawless diamonds which are not likely to occur naturally. Colorless or white diamonds are extremely rare and all diamonds have flaws which make them unique. Apollo diamonds will look perfect but they are not likely to be original.


So for color: synthetic diamonds are can be rare color stones which were more rare and expensive based on how rare they were in mines. [Apollo Diamond and Carnegie Institute can make colorless diamonds] Yellow diamonds are cheaper, but amber and other colors can be more expensive.



For cut: this is a factor of the gem cutters skill and the popularity of the style.

For carat: Synthetic diamonds can be bigger than virtually any mined diamonds.
Clarity: From 2006, 2007, the GIA studied 43 Apollo diamond stones. Statistically a 1 carat is one in a million diamonds mined, and a 2 carat is one in five million diamonds mined.



The CVD synthetic diamonds examined for the study weighed between 0.14 and 0.71 cts. The near-colorless goods ranged from E to M on the GIA color scale. Fourteen were fancy colors—11 orange to pink and three dark brown. The samples covered the clarity scale from VVS to I, though the majority were in the VS range.


How much does "color" affect cost?
Let's start with a 1.00 carat diamond of K color and VS1 clarity. If you move up to an H color, you will pay approximately an extra $1,700 per carat. Move up to F color, the increase will be approximately $1,100 per carat. Improve the color to D and the increase will be approximately $900 per carat.

80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually) areunsuitable for use as gemstones and known as bort, are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 metric tons) of synthetic diamond is produced annually for industrial use.

In 2006, the annual production of gem quality synthetic diamonds was only a few thousand carats, whereas the total production of natural diamonds was around 120 million carats. Although the production of colorless synthetic diamonds is dwarfed by that of natural diamonds, one can only find one fancy colored diamond for every 10.000 colorless ones. Since almost the complete production of synthetic diamonds consists of fancy diamonds, there is a high probability that the larger fancy colored diamonds (over 1.5 carats) will be synthetic.






Since 2005, the same institute has theoretically been able to make 300 carat diamonds using chemical vapor deposition.

The diamonds were grown directly from a gas mixture by the chemical vapor deposition (CVD) process at a rate that is up to 100 times faster than other methods used to date.

In 2005, the Carnegie Institute's Geophysical Laboratory could produce 10 carat (2 g) single-crystal diamonds rapidly (28 nm/s) by CVD, as well as colorless single-crystal diamonds. Growth of colorless diamonds up to 60 g (300 carats) was believed achievable using their method.



FURTHER READING
The Cullinan diamond was the largest gem-quality diamond ever found, at 3,106.75 carats (621.35 g or 1.3698 pounds).


Glass copies of the nine diamonds cut from the Cullinan

The largest polished gem from the stone is named Cullinan I or the Great Star of Africa, and at 530.2 carats (106.04 g) was the largest polished diamond in the world until the 1985 discovery of the Golden Jubilee Diamond, 545.67 carats (109.13 g), also from the Premier Mine. Cullinan I is now mounted in the head of the Sceptre with the Cross. The second largest gem from the Cullinan stone, Cullinan II or the Lesser Star of Africa, at 317.4 carats (63.48 g), is the fourth largest polished diamond in the world and is also part of the British crown jewels, as it forms a part of the Imperial State Crown.



Chemical vapor deposition of diamond at wikipedia

Synthetic diamonds at wikipedia

The largest synthetic diamond crystal grown to date via high-pressure, high-temperature (HPHT) crystal growth chambers was a 34-carat yellow stone. Apollo Diamond is a company that currently produces gem diamond through chemical vapor deposition and sells clear diamond gemstones.


The 45.5 carat Hope diamond at the Smithsonian Institute has been valued at about $250 million.

Synthetic diamond production volumes.

HTHP (High Temperature High Pressure) Method
In 2007, there were about 300 world fleet of BARSes included about 300 devices in the world. The main owners are 1) Adamas BGU (Minsk) – 150 118 (only 60 in operation36 more are being installed); 2) the USA U.S. company Gemesis – 100 devices; 3) company High Optical Technologies company (Moscow) – 30 devices.
A typical process of one carat diamond synthesis takes about 100 hours, and unique processes take up to 300 hours (sometimes 5-6 carat diamonds can be produced).


Gemesis' carat production [2008] averages about 100,000 carats per year. Five to six times the production levels from two years ago. [Total mined gem production totals nearly 30 million carats (6000 kg) of cut and polished]. And the average size of the Gemesis diamond also has increased; the company is now producing polished stones as large as 2.75 carats. Gemesis will be announcing its pink diamonds soon perhaps by the end of 2008, with blue diamonds slated to follow about six to nine months later.

CVD Method
The most popular companies using this technology are: Element Six (De Beers affiliate), Apollo Diamond (USA), and the geophysical laboratory of the Carnegie Institute. There are an estimated 100 CVD synthesis plants in the world and the majority are technically oriented.
Only Apollo Diamonds is aimed at jewelry; — the USA Today reported that Apollo Diamonds has 5 five synthesis plants, which can produce 5 carats per week. The equipment allows for producing the production of mainly of brown diamonds from bright to dark colors.


NOTE: The new Carnegie Institute process can easily and cheaply upgrade brown CVD diamonds to good quality gems.
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