Engraved gem

An engraved gem, frequently referred to as an intaglio, is a small and usually semi-precious gemstone 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. 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; when referring to monumental sculpture, the term counter-relief, meaning the same as intaglio, is more likely to be used. Vessels like the Cup of the Ptolemies and heads or figures carved in the round are also known as hardstone carvings. 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. 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.

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Julia Schmale, Ivo Fabio Beck, Hélène Paule Angot

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting ...

2023

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Tracking Articulated Bodies using Generalized Expectation Maximization