Dr. Yuan on Diamonds: The Color Problem of CVD Cultivated Diamonds
Release time:
2021-07-14 00:00
The color of CVD cultivated diamonds has great troubles for all producers and markets. With fast growth speed, the color of CVD cultivated diamonds will appear brown. After high temperature, high pressure or low pressure and high temperature color change, brown will be reduced or eliminated, but most CVD diamonds from manufacturers will be gray and black. There are about 100 CVD growth factories in the world, only a few of which can directly grow white or change color to become positive white. Very few factories, some are white and some are grayish black. Most other factories cannot be white. Very slight brown and gray diamonds can still be sold at low prices, while the more obvious brown and gray-black diamonds have to be irradiated and sold in other colors. Several experiences in selling colored cultivated diamonds in history ended in failure: high-temperature and high-pressure cultivated diamonds grown in Russia more than 30 years ago were changed to colored diamonds and sold in Thailand under the name of Tairus. Gemesis companies in Florida, USA, which ended in 2012, grew yellow high-temperature and high-pressure cultivated diamonds from Russian equipment and irradiated them into various beautiful colors. Both of these times are applauded but not popular, and everyone loves it, but the market acceptance is low and it cannot be sold in large quantities. At present, after the diamond cultivated by high temperature and high pressure and CVD is changed into color, there is some market demand for better-looking color, but compared with regular white, the ratio is still very low, and the color that is not good-looking is difficult to sell and will remain in stock for a long time. If a factory can only do color, will not be able to survive, must try to do a large number of positive white, with a small number of failed white cultivation diamonds, into color, as a by-product sales.
CVD cultivated diamonds show gray and black after color change, and there are many factors. Careful analysis includes the following 15 kinds: the structure of the machine, the material of the machine, the sealing effect of the cavity, the purity of the gas, the mutual ratio of various gas flows, the growth rate, the size of the cavity pressure, the size of the plasma power, the growth temperature, The color of the diamond crystal, the distance between the seed crystal and the plasma, the shape of the plasma and the density of different positions, the stability of the plasma, and the temperature of the cooling water.
The above factors will affect the color of CVD cultivated diamonds, but some of them have a great influence and have a small influence. They must be completely solved in order to get positive white. The colors with the largest demand in the international market are F, G, and H colors, and the demand for higher or lower colors is less. Color is the main improvement target of CVD jewelry cultivation diamond industry.
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