Diffusion Confusion: More on Treated 'Padparadschas'

By Gary Roskin, G.G., FGA, Senior Editor -- JCK Online, 4/1/2002 2:00:00 AM

Last month we reported on a study conducted by the American Gem Trade Association Gem Testing Center that found that certain sapphires coming out of Bangkok had been diffusion-treated to make them look like padparadschas. The lab reports that "the orange component of the apparent overall color of this stone is due to artificial surface diffusion." AGTA also notes that repolishing may remove the diffused orange color. (See " 'Padparadschas' Are Diffusion Treated," JCK March 2002, p. 24.)

The Gemological Institute of America's Gem Trade Laboratory, with help from Richard Hughes at Pala International, examined close to 50 of these gems. According to this study, while researchers could not confirm introduction of a trace element, they did find a color layer that takes on the shape of the faceted or preformed gem.

Dr. John Emmett, president of Crystal Chemistry in Brush Prairie, Wash., suggested that if there is a trace element involved in the color creation, it could be magnesium, which—in minor amounts—may not be detectable with current testing methods. More recent work by GIA has found high concentrations of beryllium, confined to the outer color layer. Until more is known, GIA's Gem Trade Laboratory will identify the sapphires as enhanced by heat and note that "the orange color of this stone is confined to a near-surface layer."

The gem producers in Bangkok and Chanthaburi say they do not diffusion-treat these gems. They say they use only heat, with additional oxygen (commonly used to boost furnace temperature) but no chemical additives. Because they don't introduce any additional metal elements—such as chromium, iron, or titanium, which are used with blue diffusion-treated sapphires—they say their new treatment method should not be considered a diffusion process.

Until researchers determine the exact method of treatment and how to describe and define it, retail jewelers should check padparadschas for diffusion treatment by examining them during immersion. The typical appearance under immersion will show a surface-based orange color layer with a pink center. Unlike the blue titanium/iron diffusion-treated sapphires, the facet junctions do not stand out under immersion.

For information on GIA's research, log onto www.gia.edu/news/insider.cfm. For more detail on heat treatment, visit the Web site of Dr. Ted Themelis, author of The Heat Treatment of Ruby and Sapphire (1992) at www.themelis.com.