Artificial Metallic Veining Enhances Manufactured Gem Materials
The Carlsbad laboratory recently examined one purple and one greenish blue cabochon (26.24 and 6.11 ct) with gemological properties and mid-IR spectra that were consistent with those of impregnated composite turquoise. Both samples contained artificial metallic veining composed of fine flattened particles suspended in a plastic. Similar-appearing material was recently reported by G. Choudhary in the Summer 2010 G&G (pp. 106-113), but the metallic veining was not identified. Analysis of the veins with EDXRF spectroscopy identified the yellow metal in the greenish blue cabochon as copper, and the white metal in the purple cabochon as zinc. By contrast, natural turquoise occasionally contains black or brown veins of limonite and grains of pyrite.
This type of artificial metallic veining was also seen recently in imitation lapis lazuli. Diane Hankinson (Carlsbad, California) loaned us a 36.43 ct pierced carving of what she assumed to be natural lapis lazuli. The testable gemological properties were in the range of those for natural lapis lazuli, but magnification revealed a manufactured structure of finely ground blue fragments with small areas of brassy metallic veining. The veins had the same finely foliated structure as those in the turquoise described above. EDXRF analysis of the vein material confirmed the presence of copper and zinc, the major components of brass. The veins looked very similar to pyrite in natural lapis lazuli.
Adding metallic veining is surprisingly effective at creating interesting and sometimes natural-appearing manufactured gem materials. Although we have only seen this technique in composite turquoise and imitation lapis, it could readily be applied to other materials, such as gold-veined quartz or composite coral.
- Nathan Renfro and Phil Owens
GIA Laboratory, Carlsbad
Courtesy of GIA eBrief.
Last updated on September 8, 2010 by Francis M Lynch