Micro-World Gems & Gemology, Summer 2019, Vol. 55, No. 2

Curved Banding in Flame-Fusion Synthetic Sapphires


Curved banding seen in flame-fusion synthetic sapphire under short-wave UV light.
Figure 1. Curved banding is easily spotted in this flame-fusion blue synthetic sapphire when illuminated with the Magilabs deep-UV fluorescence system, a short-wave UV source. Photomicrograph by E. Billie Hughes; field of view ~13 mm.

Most synthetic ruby and sapphire on the market is grown by Verneuil flame fusion. It can usually be separated from natural corundum by its distinctive curved banding, in contrast to the angular zoning seen in natural stones. Gemologists may see these features in the microscope when using darkfield or brightfield illumination. This zoning can also be seen with use of a short-wave fluorescent light, as noted in Ruby & Sapphire: A Gemologist’s Guide (R.W. Hughes et al., Lotus Publishing, Bangkok, 2017).

Flame-fusion synthetic sapphire displays curved banding under short-wave UV light.
Figure 2. Observed with a short-wave UV light source, the sample displays curved banding, a telltale sign of a flame-fusion synthetic sapphire. Photomicrograph by E. Billie Hughes; field of view ~24.5 mm.

Recently the author noticed two excellent examples. When viewed with the Magilabs deep-UV fluorescence system (a proprietary short-wave UV source), the curved banding in the synthetics was clear (figures 1 and 2), allowing them to be easily separated from natural corundum. Gemologists using a DiamondView may see the same reaction.

E. Billie Hughes is a gemologist at Lotus Gemology in Bangkok.