Spring 2010

Featured Lab Note: Coated and Fracture-Filled Orangy Red Diamond

The New York lab recently examined a 1.09 ct round brilliant diamond with an evenly distributed, highly saturated orangy red color (figure 1). Extremely rare in nature, such high saturation is typically seen only in treated or synthetic diamonds. Viewed with magnification, though, it lacked the color zoning or graining seen in such stones. Further investigation with reflected light revealed colorless spots along the pavilion facets and facet junctions (figure 2), which indicated the presence of a coating.

Viewed face-up, the diamond fluoresced weak blue to long-wave ultraviolet (UV) radiation, and very weak yellow to short-wave UV. Both appeared patchy throughout the diamond. Viewed face-down, however, the diamond appeared inert, indicating that the fluorescence was being masked.

Infrared (IR) spectroscopy showed features typical of a type Ia diamond. The UV-visible-near infrared (UV-Vis-NIR) spectrum revealed a broad band centered at ~480 nm, typical for an orangy yellow to yellowish orange diamond, rather than a strong orangy red one such as this. With the ultra-short-wave (~225 nm) radiation of the DiamondView, we could see patches of blue fluorescence where the coating had been damaged; no coating was evident on the crown facets.

Further examination with magnification produced evidence of a second treatment. Looking at the stone through the pavilion, we saw numerous cracks that appeared to contain trapped bubbles, often the first indication that a diamond has been glass filled (S. F. McClure and R. C. Kammerling, “A visual guide to the identification of filled diamonds,” Summer 1995 G&G, pp. 114–119). Although the flash effect would normally be easy to see in a glass-filled diamond such as this one that had many large feathers, the orangy red coating masked the effect. Only with strong fiber-optic lighting could we see flash effects in this diamond, but they appeared in several areas when viewed through the crown and the pavilion. Energy-dispersive X-ray fluorescence (EDXRF) spectroscopy detected lead, which confirmed the presence of a glass filling.

As this stone illustrates, we are now seeing combinations of diamond treatments. Since neither coating nor fracture filling is permanent, only an identification report was issued for this diamond.

Sharon Cybula and Paul Johnson