ANALYSIS OF COLOR AND CLARITY CHANGE IN HEAT TREATED GEM SPINEL

The heat treatment of gemstones, in order to improve their color and clarity, is an extremely old process, possibly as old as the gem trade itself. However heat treated gem spinel has only been introduced to the market within the last decade. Through various heat treating techniques employed by this study, changes in samples of spinel have been documented and analyzed using various methods. In this study, samples of spinel rough have been heat treated at a variety of temperatures as well as in both oxidizing and reducing environments, and with the addition of various light elements which apparently have diffused into the crystals. Part of the original samples is always left unheated so the heated samples can be compared to the originals. To analyze both major and trace elements present in the samples that would affect the treatment process, x-ray fluorescence has been used. To analyze the color change in the samples FTIR spectroscopy has been used. From the XRF analysis I have hypothesized that inclusions of undissolved rutile causes the silkiness (cloudiness) in the samples. All samples experienced marked clarity improvement across the board when exposed to heat, as long as a minimum temperature was maintained for a certain time. Darker samples (purples, greens, blues) of spinel did not experience as dramatic of a color change during the heat treatment as reds and pinks. However, under appropriately controlled conditions, red and pink spinel could undergo clarity improvements with or without major color change.