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engraved gem
An engraved gem is a small gemstone, usually semi-precious,〔Fully half of the antique engraved gems in the Berlin museums and the British Museum are either sard or carnelian, Etta M. Saunders, noted (Saunders, "Goddess Riding a Goat-Bull Monster: A Ceres Zodiac Gem from the Walters Art Gallery" ''The Journal of the Walters Art Gallery'' 49/50 (1991/1992;7-11) note 19. .〕 that has been carved, in the Western tradition normally with images or inscriptions only on one face. The engraving of gemstones was a major luxury art form in the ancient world, and an important one in some later periods.〔The three preeminent European collections of post-Classical engraved gems are the Cabinet des Médailles at the Bibliothèque National, Paris, the Habsburg collection, Vienna, and the British Museum, London, O. M. Dalton observed in "Mediæval and Later Engraved Gems in the British Museum — I" ''The Burlington Magazine for Connoisseurs'' 23 No. 123 (June 1913:128-136) and "II" ''The Burlington Magazine for Connoisseurs'' 24 No. 127 (October 1913:28-32).〕
Strictly speaking, engraving means carving in intaglio, with the design cut ''into'' the flat background of the stone, but relief carvings, with the design projecting ''out of'' the background as in nearly all cameos, are also covered by the term (this article uses "cameo" in its strict sense, to denote a carving exploiting layers of differently coloured stone). The activity is also called gem carving, and the artists ''gem-cutters''. References to antique gems, and intaglios in a jewellery context, will almost always mean carved gems. Vessels like the Cup of the Ptolemies and heads or figures carved in the round are also known as "hardstone carvings" and similar terms.
Glyptics, or "glyptic art", covers the field of small carved stones, including cylinder seals and inscriptions, especially in an archaeological context. Though they were keenly collected in antiquity, most carved gems originally functioned as seals, often mounted in a ring; intaglio designs register most clearly when viewed by the recipient of a letter as an impression in hardened wax. A finely carved seal was practical, as it made forgery more difficult - the distinctive personal signature did not really exist in antiquity.
==Technique==
Gems were mostly cut by using abrasive powder from harder stones in conjunction with a hand-drill, probably often set in a lathe. Emery has been mined for abrasive powder on Naxos since antiquity. Some early types of seal were cut by hand, rather than a drill, which does not allow fine detail. There is no evidence that magnifying lenses were used by gem cutters in antiquity. A medieval guide to gem-carving techniques survives from Theophilus Presbyter. Byzantine cutters used a flat-edged wheel on a drill for intaglio work, while Carolingian ones used round-tipped drills; it is unclear where they learnt this technique from. In intaglio gems at least, the recessed cut surface is usually very well preserved, and microscopic examination is revealing of the technique used.〔Kornbluth, 8-16 (quotes passages ) from Theophilius and others, and discusses various techniques. See Theophilius's article for full on-line texts.〕 The colour of several gemstones can be enhanced by a number of artificial methods, using heat, sugar and dyes. Many of these can be shown to have been used since antiquity - since the 7th millennium BC in the case of heating.〔Thoresen, "Gemstone enhancement"〕
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