The article is a witty, informative narrative that explains sapphires that have been treated with surface diffusion treated corundums (SDTCs). It chronologically explains the history of SDTC from the original Linde patents up to the current deep diffusion treatments and how to differentiae treated sapphires with real sapphires. These treatments make the sapphires shinier and “bluer” with the right type and amount of heat and treatment. Microscopic examination of these treated sapphires using gemological microscopes would reveal color diffusions that are measurable in actual millimeters rather than a fraction of it.

Surface diffusion treated corundums (SDTC), as stated in the article, was first rumored around the 90s in Bangkok. It was originally dismissed because, back then, it was only a rumor and nobody came forward to prove its existence.

Synthetic or corundum stones and materials were first thought of and developed when World War II began. The American government’s concern was to fill out the future demand and supply of materials that could not be bought offshore due to the war. Synthetic corundums continued to be manufactured even after the war. It was also after the war that rutile silk was accidentally discovered. Rutile silk can be used to control to make synthetic star corundums making them commercially available. A series of patents were then passed and approved. These patents granted a way or method of diffusing colors just beneath a stone using the right amount of heat within the materials (titanium and other coloring oxides) using gemological microscopes. Gemological microscopes are useful in studying these stones.

The effect of making these corundums commercially available is tremendous in the gem market. The process of making these synthetic stones spread throughout the world and many clever people made adjustments to the process until the “perfect” treatment result was achieved. Unsuspecting buyers of these types of stones are not aware that the sapphire stones they bought from reputable dealers/sellers were treated with SDTC.

The article also mentioned ways in identifying surface diffusion treated corundums (SDTCs). One way is by using stereoscopic microscopes like a gemological microscope and using diffused light field illumination. The specimen is immersed with methylene iodide in order to stain it and making identification easier. Comparing natural and synthetic corundums, it was revealed in the article that in natural single crystals, colors form in zones or bands that are parallel o crystal faces. When the color forms along polished facets, it is not natural because the natural stone is not faceted on its development up the ground.

SDTC corundums have colors concentrated just inside the stone’s girdle and on the facet junctions. A bleeding of color along an SDTC stone with feathers, fractures, cavities, pits, or any surface breaks will positively identify the stone as synthetic.

However, the article warns SDTC testers not to approach the identification of these synthetic stones lightly. The article suggests having more than one piece of 100% synthetic SDTC corundum for future comparisons.

The article also compares characteristics between SDTC and natural heat-treated stones.Here is a link to the article