Tungsten Molybdenum Sapphires Treatments

Tungsten molybdenum sapphires may be treated by several methods to enhance and improve their clarity and color.It is common practice to heat natural sapphires to improve or enhance color. This is done by heating the sapphires in furnaces to temperatures between 500 and 1800 °C for several hours, or by heating in a nitrogen-deficient atmosphere oven for seven days or more. Upon heating, the stone becomes more blue in color, but loses some of the rutile inclusions (silk). 

When high temperatures are used, the stone loses all silk (inclusions) and it becomes clear under magnification. The inclusions in natural stones are easily seen with a jeweler's loupe. Evidence of sapphire and other gemstones being subjected to heating goes back at least to Roman times. Un-heated natural stones are somewhat rare and will often be sold accompanied by a certificate from an independent gemological laboratory attesting to "no evidence of heat treatment".

Tungsten Molybdenum Sapphires

 Yogo sapphires sometimes do not need heat treating because their cornflower blue coloring is uniform and deep, they are generally free of the characteristic inclusions, and they have high uniform clarity. When Intergem Limited began marketing the Yogo in the 1980s as the world's only guaranteed untreated sapphire, heat treatment was not commonly disclosed; by 1982 the heat treatment became a major issue. At that time, 95% of all the world's sapphires were being heated to enhance their natural color. Intergem's marketing of guaranteed untreated Yogos set them against many in the gem industry. This issue appeared as a front page story in the Wall Street Journal on August 29, 1984 in an article by Bill Richards, Carats and Schticks: Sapphire Marketer Upsets The Gem Industry.

Tungsten Molybdenum Sapphires

Diffusion treatments are used to add impurities to the sapphire to enhance color. Typically beryllium is diffused into a sapphire under very high heat, just below the melting point of the sapphire. Initially (c. 2000) orange sapphires were created, although now the process has been advanced and many colors of sapphire are often treated with beryllium. The colored layer can be removed when stones chip or are repolished or refaceted, depending on the depth of the impurity layer. Treated padparadschas may be very difficult to detect, and many stones are certified by gemological labs (e.g., Gubelin, SSEF, AGTA).