How are lab-grown emeralds made?
Lab emerald is grown from a solution, never from a melt, because beryl breaks down into other compounds before it melts: a flame turns it into glass. Two methods are used. Flux growth (Chatham, Gilson) dissolves beryllium, aluminium and chromium compounds with silica in a molten flux in a platinum crucible, and emerald crystallises on beryl seed plates over months. Hydrothermal growth (Linde, Biron, Tairus and Chinese producers) deposits emerald from a hot, pressurised water solution in an autoclave at about 0.15 mm a day, so a crystal thick enough to cut takes weeks. Both are slower and costlier than flame-fusion sapphire, which is why lab emerald costs more per carat.
Why emerald cannot take the flame
Emerald is beryl, Be3Al2Si6O18, coloured green by chromium or vanadium. Beryl melts incongruently: heated far enough it breaks into other compounds before becoming a liquid, so Verneuil's flame produces glass instead of a crystal. That is why lab emerald arrived decades after flame-fusion ruby.
Flux growth: Chatham and Gilson
The ingredients are dissolved in a molten flux, most often lithium molybdate or lithium vanadate, in a platinum crucible, and emerald crystallises on seed plates. Chatham says a crop takes about a year. Flux emerald contains no water in its structure. Carroll Chatham grew his first crystals in 1935 and had a repeatable process by 1938.
Hydrothermal growth
Union Carbide's (Linde) 1964 patent describes an autoclave at 425 to 800 C and 7,000 to 30,000 psi with a fluoride solution, growing emerald on colourless beryl seed plates. Commercial growth is about 0.15 mm a day. Hydrothermal emerald reached jewelry in 1960; Russia became the major producer in the late 1980s and 1990s, and Tairus is the leading name now.
How a lab tells them apart
Flux emerald shows wispy flux-filled fingerprints, small phenakite crystals and platinum platelets, and reads slightly low on a refractometer. Hydrothermal emerald shows chevron growth zoning, cone-shaped "nail-head" spicules and seed-plate remnants, and chlorine features in the infrared spectrum never seen in natural emerald.
History
French chemists made the first millimetre-size emerald crystals in 1888 and 1890; Richard Nacken grew flux emeralds in Germany in 1923 to 1925; IG Farben sold "Igmerald" from 1935 to 1942; Chatham production began in the US in 1941.
Frequently Asked Questions
How long does it take to grow a lab emerald?
Weeks for hydrothermal growth at about 0.15 mm a day, and up to about a year for a flux crop by Chatham's account; flame-fusion sapphire is far faster and cheaper.
Why is lab emerald more expensive than lab sapphire?
A platinum crucible or a pressurised autoclave running for weeks or months costs far more than a flame-fusion furnace.
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