K. Schmetzer, H.-J. Bernhardt, W. A. Balmer, and T. Hainschwang. “Synthetic alexandrites grown by the HOC method in Russia: Internal features related to the growth technique and colorimetric investigation,” Journal of Gemmology, Vol. 33, No. 5–6, 2013, pp. 113–129. Photo courtesy of Karl Schmetzer.
Figure 1. The illustration demonstrates the three optical effects studied in the article: Pleochroism, the alexandrite effect, and the Usambara effect. Represented are two oriented cubes of HOC synthetic alexandrite with edge lengths of 3mm and 8mm viewed in unpolarized daylight and incandescent light down the a-, b- and c-axes. With identical lighting and edge length, pleochroism is clearly seen. The alexandrite effect is illustrated by comparing same size cubes along the same axis but under different lighting. Comparing the two different cubes under the same lighting and orientation, the Usambara effect is observed. Photos and artwork by Karl Schmetzer.
A 43-carat alexandrite in the collection of the British Museum.
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