Dr. Yuan:Color Problems of CVD Lab-grown Diamonds

专栏 · 苑博士讲钻石

Column: Dr. Yuan Chat Diamonds

The color of CVD Lab-grown diamonds is a great Problem to Lab-grown all producers and the market. When the growth rate is fast, the color of the CVD Lab-grown diamonds will appear brown. After HPHT or LPHT, the brown will be reduced or eliminated, but most manufacturers' CVD diamonds will have gray and black colors. There are about a hundred CVD growth factories in the world, only a few can directly grow white or enhance the color to become true white; a few other factories are partly white and others are gray-black; most of the other factories cannot achieve true white . Very slight brown and gray diamonds can still be sold at low prices, and the more obvious brown, gray and black diamonds have to be irradiated and sold in other colors.

Several experiences in the history of selling colored lab-grown diamonds have all ended in failure: 30 years ago, the HPHT lab-grown diamonds grown in Russia were enhanced to colored and sold under the name Tairus in Thailand. Before 2012, the Gemesis in the United States grew yellow by Russian HPHT equipment. And then irradiate into various beautiful colors. Both times were applauded but not popular, everyone loved, market acceptance was low, and mass sales were not possible.

Nowadays, there is some market demand for HPHT and CVD lab-grown diamonds to enhance to colors, but compared with true white, the ratio is still very low. If a factory can only achieve color diamonds, it will not be able to survive. We must try to achieve a large amount of true white. With a small amount of failed white lab-grown diamonds, enhance to color diamonds and sell as a by-product.

CVD-grown diamonds show gray and black after HPHT treating their color. There are many factors that can cause them. The following 15 kinds of factors are carefully analyzed:

1) the structure of the reactor
2) the material of the reactor
3) the sealing effect of the reactor
4) the purity of the gas
5) the flow rate of mutual ratios of various gases
6) growth rate
7) chamber pressure
8) plasma power percent
9) growth temperature
10) the color of the diamond crystal during growth
11) the distance between the seed plates
12) the distance between the diamond crystal and the plasma
13) the shape of the plasma and the difference location of plasma density
14) plasma stability
15) cooling water temperature.

The above factors will all affect the color of CVD-grown diamonds, but some have a large impact and some have a small impact, and must be completely resolve to obtain a true white color. The colors with the largest demand in the international market are F, G, H colors, and the demand for higher or lower colors is less. Color is the most important improvement target in the CVD jewelry Lab-grown diamond industry.

Author

Joe Chih-Chung Yuan, Ph.D. from Sun yat-sen university, Director of Henan Godiam New Material Technology Co., Ltd. Engaged in diamond cutting , identification, researching teaching and growing for more than 44 years. Currently engaged in diamond jewellery cutting, high temperature high pressure(HPHT), chemical vapor deposition (CVD) single crystal, polycrystalline diamonds growing, application researching and production. Established laboratories and diamond cutting and growing factories in New York, Taipei, and Zhengzhou.

- Obtained the GIA Graduated Gemologist G.G.
- Obtained the D.G.A diamond membership and tutor qualification of British Gem-A.
- Dozens of new diamond design patterns and invention patents in various countries around the world
-In 2009, became a delegate of the International Gemmological Conference(IGC), the highest gemmologjcal conference in the world.
- Hundreds of presentations and dozens of papers in Chinese and English in professional journals in various countries.
-  Publication: "Diamond Researching" was published in New York, USA in 1999.

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