Science: Sapphires for Everybody

Ever since the Pharaohs, men have been getting cleverer & cleverer at making imitation gems. Almost every precious stone now has a man-made twin. Last week the Linde Air Products Co. (a unit of Union Carbide & Carbon Corp.) announced that it had finally produced “star” sapphires and rubies.

Ordinary sapphires and rubies are clear crystals of aluminum oxide (A12O2). The colors come from small amounts of such elements as chromium or iron. For years, both gems have been manufactured (without the stars) by passing finely powdered A12O2 through the flame of an oxyhydrogen blowpipe. The tiny particles melt and then solidify into a crystalline blob just beyond the flame. Such crystals have all the beauty, color, hardness and other desirable properties of natural gems. When they are well made, their “falsity” can be detected only by an expert who looks (with a microscope) for their slightly curving “growth lines.”

Star sapphires, which have a brilliant, six-pointed star, are more difficult to imitate. Their “asterism” comes from minute particles of some foreign matter (some authorities claim that it is empty space) arranged symmetrically throughout the crystal structure. These form a slight cloudiness (jewelers call it “silk”) which reflects light in the shape of a star.

In the great gem hall of New York’s American Museum of Natural History last week, Linde chemists displayed synthetic star stones that were red, blue, violet, soft grey and pink. No two were exactly alike, but through the high, rounded surface of each twinkled a six-pointed star. The biggest stone, a star ruby, was as big as a walnut shell and weighed more than 100 carats (.643 troy oz.). Beside the synthetics, many of the natural stones from the museum’s collection looked pallid.

The Linde Co. is not telling exactly how it makes its star stones, but admits to using a modification of the standard blowpipe system. The synthetics will sell for a comparatively low price (in the hundreds), but Linde does not think that the price of natural stones (up in the thousands) will fall very much. There will still be buyers who value rarity above beauty. Nonetheless, the woman who wears a synthetic star sapphire will be perfectly safe from detection so long as she keeps away from lapidaries with microscopes.