gems, corundum, treatments.4, titanium diffusion, sapphire, bulk diffusion

This trade commentary defends the commercial introduction of surface [bulk] diffusion-treated Sri Lankan sapphires and questions the distinction drawn by some dealers between this process and conventional heat treatment. Lumetta describes an improved technique, developed in the United States from earlier Linde diffusion technology, that reportedly increases the penetration of colour into corundum. The resulting stones combine attractive blue colour, calibrated dimensions and good cutting, qualities that the author regards as difficult to obtain together in ordinary Sri Lankan production. Drawing on published accounts of corundum colour and enhancement, the article explains blue colour through iron–titanium charge transfer and describes treatment by heating stones in contact with colouring compounds so that titanium enters their surface layers. The author contrasts this addition of colouring elements with heat-treatment processes that modify existing constituents or their oxidation states, arguing that both approaches enhance appearance and that commercial opposition to diffusion reflects unequal access to technology and competing financial interests. This equivalence is presented as the author’s position rather than demonstrated through experimental comparisons. Surface diffusion-treated stones are placed between lower-priced synthetic corundum and more expensive Sri Lankan sapphires whose colour is natural or improved by conventional heating. Lumetta considers better-quality Thai sapphires their principal price competitors, with colour preference influencing purchasing decisions. He rejects predictions that the new product will depress sapphire prices generally and instead suggests that independently certificated fine sapphires may gain value through clearer differentiation. Disclosure is central to the argument: earlier diffusion-treated stones had sometimes circulated without identification, whereas the products discussed are explicitly marketed as treated material. The author acknowledges his involvement in their marketing through Gem Source in Las Vegas, where stones are offered in calibrated sizes, several cutting styles and graded colour categories. Their intended customers include larger jewellery manufacturers requiring a consistent supply of matching stones. The article predicts consumer acceptance on the basis of colour, cutting and price, presenting diffusion-treated natural sapphire as a distinct commercial alternative whose place in the market depends on transparent description and product differentiation.