Diamond Rival

In some respects, the new "diamonds" made of titania (titanium dioxide) are better than the real thing./- Last week three advertisements in the New York Times Magazine offered cut stones "more brilliant than diamonds" at prices ranging from $10 to $16 a carat (price of first-grade white diamonds: about $1,100 for a one-carat stone). One ad suggested: "A handsome engagement ring made of our remarkable gem presented to any girl will win her devotion. The hundreds of dollars saved will go far toward building a permanent home."

Titanium dioxide is found in nature in black or brown crystals known to mineralogists as "rutile." When the pure oxide, finely powdered, is fed through an oxyacetylene flame, it collects in a solid, carrot-shaped "boule." At first the boule is black, but careful heating turns it to a very faint yellow, the color of good-quality "Cape diamonds." Stones of almost any color, including blue, green and deep yellow, can be made by doctoring the oxide with small amounts of impurities.

Titania's close resemblance to diamonds is due to its index of refraction, i.e., its ability to bend light rays. This property makes a stone glitter. Diamond's index of refraction is extremely high: 2.42. Titania's index is higher: 2.62 to 2.90. Even more important is its "dispersion," i.e., its ability to break white light into rainbow colors. Diamond disperses light twice as much as common glass does, but titania disperses it seven times as much. So far, titania cannot be made absolutely white (many valuable diamonds are not white, either), and it will never rival diamond in hardness.

Those who cherish diamonds because of their high cost (owing to the tight control of the South African diamond monopoly) will not welcome the development of titania. But in sparkle and "fire," it surpasses its rival and may force the merchandisers of genuine diamonds to warn their customers against too much "fire."

/-Synthetic sapphires and rubies are made artificially of aluminum oxide, are therefore the same chemically as their natural counterparts. Natural diamonds consist of carbon, so gems of titanium dioxide cannot be called "synthetic diamonds."

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