A treatment that enhances the color of corundum (rubies and sapphires) is known as diffusion treatment. Diffusion treatment entails exposing the stone to certain chemicals combined with high heat in a furnace. This treatment allows unimpressive gems to be transformed into beautiful stones with vivid color. For example, overly dark or pale sapphires that are diffused can exhibit desirable cornflower blue, intense orange or canary yellow colors. Since this treatment cannot be discerned by merely looking at the gemstone, it is important that gem dealers practice full disclosure. As long as buyers are made aware of diffusion treatment, it is widely accepted as a permanent and stable enhancement for colored gemstones. Diffusion not only allows rare and beautiful stones to be purchased at more affordable prices, but it has also enabled the gemstone industry to continue and thrive in Thailand, where experts have honed this gemstone enhancement.
Traditional diffusion treatment is more readily accepted for star sapphires. Indeed, diffusion treatment is a popular method for treating star sapphire, since the treatment will increase the asterism (the star effect in sapphire and ruby). The process enhances the star effect on the gemstone and the stone can be sold as a diffused star sapphire. The hardness of the gemstone is not affected by the diffusion process, therefore the gemstone retains its original physical properties. Diffused star sapphires should not be polished for a second time or recut because the treatment is only on the surface of the stone. Polishing or recutting would remove this surface treatment. However, most buyers never repolish or recut the gemstones set in jewelry. This is especially true of sapphires because they are hard, scratch-resistant gemstones.
Through old methods, generally, only the surface color changed, so if you sliced the gem in half, the inside of the stone would be a different color, usually a paler, less valuable color. The problem was that the new surface color was not very deep; and only penetrated about half a millimeter. If the stone was damaged or perhaps recut, then the original, undesirable color would be noticeable. These methods are therefore referred to as "surface diffusion". More modern diffusion treatment using beryllium (also referred to as "lattice diffusion") penetrates throughout the stone, allowing for full and permanent enhancement. Nowadays, this method is used to change the color of sapphire. Usually the original material is a dark, pale or almost colorless stone that is treated to change the color. Reputable dealers will always tell you which stones have been altered by this method of treatment. In order to distinguish between old and new diffusion methods, GemSelect sells stones that have been subjected to the traditional diffusion treatment as "diffused"; and beryllium-diffused gems as "Be heated".
The decision as to whether to buy in an untreated gemstone or a diffused gemstone will depend on several factors, such as budget, availablity and personal preference. Seller trust and full disclosure of diffusion and other gemstone treatments allows the customer to make an informed choice and acquire their desired gemstones with peace of mind.
- First Published: September-04-2006
- Last Updated: December-26-2016
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