Nice little gem... The technique used to get the white in the engraved depression relates to that used from very ancient times (etched carnelian beads from ancient Mesopotamia) to more recent Tibetan Dzi beads. The carnelian was shaped and engraved. Next it was covered in an alkali solution (probably sodium carbonate) and heated. This bleached the surface. The upper surface of the gem was then re-polished to leave the white in the depressions. There were several variations, for example the gem could be whitened and then engraved, leaving the engraved design against a white field. Quite well known in Roman times, but often misdescribed (sometimes as burnt). I think the white upper surface on the grey-black Roman nicolo gems were often created this way. The white surface is very resistant to change with time and in fact in alkali burial environments, ancient carnelian and agate beads can gain a natural whitened surface.
Posted on: Sat, 16 Aug 2014 11:25:42 +0000
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