Consumers are finding it harder to distinguish synthetic diamonds from the real rocks. Since the 1950s scientists have grown imitations by depositing carbon atoms onto tiny natural or synthetic seed diamonds, under high pressure and temperature. But ever finer control of the temperature gradient around the seed is eliminating the telltale imperfections that jewelers could once detect with a magnifying glass.

The synthetic approach builds up the seed slowly to prevent metal atoms needed for the process from being trapped in the growing stone, which causes noticeable inclusions. It takes up to a week to assemble a one-carat stone. Diamonds for industrial cutting tools can be grown faster, because inclusions do not reduce hardness. Polycrystalline diamond coatings for tools are laid down using chemical vapor deposition.

This article was originally published with the title Carbon Copy.

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