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GSI Cautions Over Color Instability in CVD Diamonds

December 05, 19

(IDEX Online) - Laboratory grown diamonds grown using the chemical vapor deposition (CVD) process could be prone to extreme color instability warns Gemological Science International (GSI).

During standard testing by GSI, a 2-carat CVD diamond was exposed to high-powered UV rays and went from near colorless to blue color. It was then returned to the vault. When it was taken out a week-and-a-half later, it had retained the blue color. 

While CVD diamonds can undergo color changes under UV light or extreme light, they typically return to their normal color after 30-60 minutes of direct sunlight.

This stone, however, took two-and-a-half hours to regain its normal color.

Based on this finding, GSI recommends that while most diamonds will not change to this extent, all lab-grown CVD diamonds should be placed in a full-spectrum light box for at least 30 minutes before color grading.    

According to GSI Chief Information Officer Nicolas Del Re, color changes may happen through casual use as well.

"When wearing out in the open, CVD diamonds may change in coloration upon even subtle exposures to electromagnetic radiation such as UV rays on a sunny beach or under a blacklight in a nightclub for example." 

The changes occur because of photochronism. This is when electrons in defects within a CVD diamond cause the energy state to change and affect the way color is absorbed on the visible spectrum, explained Del Re.

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GSI对CVD钻石颜色不稳定性的警告

19年12月5日 ，IDEX在线员工记者

（IDEX在线）-国际化学宝石学会（GSI）警告说，使用化学气相沉积（CVD）工艺生长的实验室种植钻石可能极易出现颜色不稳定性。

在GSI进行的标准测试中，将2克拉CVD钻石暴露于高功率紫外线nd从几乎无色变成了蓝色。然后将其返回金库。一周半后取出时，它保留了蓝色。 

虽然CVD钻石在紫外线下会发生颜色变化在极端光线下，它们通常会在直射阳光下30-60分钟后恢复其正常颜色。

然而，这块石头花了两个半小时才能恢复其正常颜色。

基于这一发现，GSI建议尽管大多数钻石都不会改变到这个程度，但所有实验室种植的CVD钻石应在全色灯箱中放置至少30分钟，然后再进行颜色分级。    

据GSI首席信息官Nicolas Del Re称，随便使用也可能发生颜色变化。

“当裸露地磨损时，即使在阳光明媚的海滩上，即使是微弱地暴露于电磁辐射（例如紫外线）下，CVD钻石的颜色也会改变。例如，在一家夜总会的黑夜里。 

发生变化是由于光时变。这是当CVD金刚石中的缺陷中的电子导致能态改变Del Re解释说，这会影响颜色在可见光谱上的吸收方式。