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A way of turning inferior, brown diamonds into rare and expensive neon
yellow-green stones is being patented by the General Electric Company (WO
01/14050). The starting point is a supply of cheap diamonds, with “impurity
clusters” of four nitrogen atoms each. These stones are encased in refractory
material and consolidated into pills. The pills are then heated and compressed,
with the refractory coating spreading the load. Under pressure, the nitrogen
atoms rearrange into smaller clusters, which fluoresce in ultraviolet light.
When you break the coating the diamonds look yellow-green in daylight, and sell
for a much higher price.