专栏 · 苑博士讲钻石
Column: Dr. Yuan Chat Diamonds
The production and market conditions of colored lab-grown diamonds are similar to the conditions of artificial color enhanced on natural diamonds. The as grown lab-grown diamonds have poor color or clarity and are not suitable for selling directly as white diamonds, that is, poor quality diamonds to artificially modify the color. For example, if the light brown to medium brown color or clarity with cloudy or flawed diamonds, these diamonds are not suitable for sale as white diamonds which are enhanced with irradiation, HPHT treatment or heat treatment, they will be enhanced into various colors, and then sell.
Causes of Diamond color
A. Impurity elements:During the diamond formation process, other elements enter, causing some impurities.
1) Nitrogen: Nitrogen is the most common impurity element in diamonds, replacing carbon atoms and entering the crystal lattice. It absorbs the purple and blue areas, emits yellow light, and is divided into Ib mono-nitrogen, IaA di-nitrogen, IaB tri-nitrogen, tetra-nitrogen, and flake nitrogen.
2) Boron: Boron replaces carbon atoms and enters the crystal lattice. It absorbs the yellow light area and emits blue light, the type is IIb.
3) Hydrogen: The hydrogen atom body is very small and can enter the gaps inside the diamond. Natural diamonds, if they contain a lot of hydrogen, present a gray tone. The hydrogen of CVD diamonds has been driven out during the HPHT enhancement of color, but the gray color that it appears later is not formed by hydrogen.
B. Plastic deformation: After natural diamonds are formed, they are subjected to high pressure to produce line or surface lattice dislocations as plastic deformation. The most common colors are: brown, pink, red, etc. During the growth of CVD diamond, due to the negative pressure, the entire diamond interior is filled with plastic deformation caused by stress, resulting in brown.
C. Point defects: Diamonds are irradiated by radioactive materials, causing protons、neutrons in the carbon nucleus or electrons in the outer ring to generate vacancies or lattice dislocations. Common colors are green, blue, and black. After HPHT or heat treatment, it will produce Yellow, pink, red, etc.
The causes of the various colors of colored lab-grown diamonds
A. Direct growth
1) Yellow: The HPHT method directly assembles raw materials to grow in the air. Because the air contains 78% nitrogen, it will grow brownish Yellow. If you add some metal elements, you can reduce the brown and get light yellow, medium yellow, or golden yellow.
2. Blue color: Adding aluminum, titanium and other nitrogen removal agents to HPHT growth raw materials, and adding boron at the same time, will produce blue color. The addition of boron during CVD growth will also produce blue color. Both blues are grayish blue, not bright enough, and not pleasing.
B. Irradiation to enhance color and heat treatment
1) Blue, green, black: all kinds of radiation sources can be used to irradiate to enhance the color, but some of the effects are too slow, such as cobalt 60; some radiation residues are too strong, such as fast neutrons emitted by nuclear reactors. Now the gem industry needs to irradiate the high-energy electrons produced by electron accelerators with extremely short irradiation residual time, the equipment and irradiation costs are low.
Excessive irradiation will produce extremely dark blue and dark green, which look black.
2) Yellow, pink, red: the blue and green obtained by irradiation can be heat treated with HPHT, under atmospheric pressure at hundreds to one thousand Celsius degrees as low to high temperature, depending on the trace elements contained in the original diamond. If it contains a small amount of mono-nitrogen, it can give a pink color, if a large amount of mono-nitrogen can give red to dark red colors.
If the CVD lab-grown diamond grows brownish, it must first be reduced or eliminated by HPHT. If the result is pure white, the owner will sell it as a white diamond. If you use a white diamond to enhance the color by irradiation, you will almost always get a good bright color.
When the color is enhanced by irradiation, the depth of the color entering from the diamond surface, depending on the irradiation measurement and time, is about 1~3mm. The color is enhanced by normal irradiation, can be implemented after the diamond is cut and polished, and the surface of the diamond will not be damaged. HPHT treatment will weaken or eliminate the brown color of the entire diamond, but will burn the surface of the diamond. Generally, HPHT enhance is performed after blocking, and it needs to be polished again after completion.
The sales of natural colored diamonds are about a few thousandths of that of white diamonds, and the sales of lab-grown colored diamonds are about a few percent of that of white diamonds. But when enhancing to colors, most of them are not good colors, such as pink with some brownish or purplish tones, not pretty good pink. The blue color obtained by adding boron during growth is grayish blue, that is, ink blue, which is not bright. For bad colors, the price will not be high, and there will be a high percentage of inventories to the owner.
The blue diamonds, pink diamonds and white diamonds that De Beers sells are all at the same price, and their colored diamonds are all good in color. The reason is that the diamonds they used were originally white diamonds or very light brown or gray diamonds, so they enhanced the colors are all good. Other manufacturers, especially CVD lab-grown diamonds, can still sell very light brown and gray diamonds as white diamonds, they enhance darker brown and gray diamonds to color diamonds. Therefore, the color of colored diamonds with a relatively high ratio is not good. Therefore, there are quite a lot of colored diamonds leaving on their hands. The industry must find ways to avoid this situation.
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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