Synthetic Emeralds Grown by W. Zerfass: Historical Account, Growth Technology and Properties

摘要

Rough and faceted synthetic emeralds were produced by W. Zerfass in Idar-Oberstein, Germany, between 1963 and 1973. The synthesis process was developed in cooperation with the chemist G. H. Jaeger; experiments started in 1952 and led to samples of facetable size in the early 1960s. Microscopic examination and chemical analysis of rough and cut Zerfass samples indicate that crystal growth took place on oriented seed plates cut from synthetic emerald crystals within a molybdate melt. Only chromium was added to the nutrient as a colour-causing trace element. Although the growth method was similar to that developed by H. Espig in the 1930s and applied by the IG Farben company, the process used by Zerfass and Jaeger was developed independently and, contrary to certain statements in the gemmological literature, did not involve anyone who had formerly worked with Espig at the IG Farben plant in Bitterfeld, Germany.