MICROQUARTZ GEMSTONES FROM THE EASTERN ROMAN EMPIRE

Remnants of materials used during the engraving process of eight hard microquartz gemstones from the Eastern Roman Empire reveal that the engravings were made by drill-wheel rotational lathes of bronze and iron. Brass drill-wheels (0.1-3 mm in size) were also used by lapidary craftsmen in the engraving process during that period. In order to facilitate the grinding process an abrasive grit (50-100 um in size) was used. A lubricant consisted of small spherical grains of tin, lead and barite that held the abrasive material together in a matrix. Thin and straight grooves were probably made with corundum or a diamond-tipped instrument. Iron oxides were fixed to the gemstone by “glue” composed of calcium, phosphorous and carbon; this material was used to paint carnelian surfaces. Limestone and barite were probably used as a paste or paint that filled in engraved lines, thus emphasizing the pictorial patterns for decorative purposes. Furthermore, gold (pure or alloyed) and silver were also used to decorate engraved motifs in gemstones at times in conjuncture with the paint. This technique resulted in attractive jewelry which suggests that gemstones were highly valued for their decorative rather than just for their monetary and protective values.