Methods of Engraving


Methods of Engraving

The choice of cutting tools and techniques was determined by the nature of the object to be engraved. Only soft stones and metals could be worked free-hand with cutting tools. In the Greco-Roman period hard stones were mostly used, which required the wheel technique. Pliny and Theophrastos give brief accounts of the methods used for producing intaglios and cameos. Our knowledge of the tecniques used can also be deduced from the stones themselves and from modern methods.

Manageable pieces had first to be chipped from a block of raw stone. These were then shaped into blanks by grinding them against a fine abrasive wheel which was worked with a treadle like a lathe. Once the gem had been ground to the desired shape, it was polished with emery dust and then, to give it a glossy lustre, with finely powdered haematite (iron oxide). The polished blank was then engraved with the aid of drills made of copper and dipped in a mixture of oil and an abrasive. These drills were mainly of the bow-drill type, either hand-held or fixed. A string was wound around the shaft of the drill and the rigid bow was drawn back and forth. A representation of such a bow-drill fixed on a horizontal lathe has survived on the gravestone of the eighteen-year-old daktulokoiloglyphos, 'the cutter of intaglios', Doros of Sardis, which dates from the second century A. D. and was found at Philadelphia in Lydia. No ancient drill has survived, but useful information can be gained from the study of traces left in the intaglios themselves.

These drills were made of iron or copper-alloy and their grinding power was greatly enhanced by the use of an abrasive such as emery (an impure form of corundum with a hardness of 9), sources of which existed in Naxos in the Cyclades, southwest Turkey, and India.

The gem engraver used a combination of drills of various sizes, the cutting edge of which was in the shape of either a tiny disk or a ball.

There appears to be no decisive evidence to prove that gem engravers used magnifying lenses in antiquity. But it has been suggested that the craft was handed down from father to son in families that suffered from myopia and therefore had no problem in focusing close-up. Gem-cutters, like other artisans in the Hellenistic and Roman periods, would belong to guilds and the profession was usually passed from one generation to the next. Regional schools and styles did exist, but they are imperfectly known for lack of enough provenanced material.

A document from Egypt, the so-called Stockholm papyrus, indicates that the colour of gems was artificially modified, either to enhance a tonality or to change it altogether. These manipulations were evidently aimed at increasing the value of an average gem and varied with the fashion of the moment. Pliny describes the use of honey to colour agates. This method is still used today: a dull and grey-looking onyx is placed in boiling honey or sugared water, so that the sugar penetrates the stone and when heated is carbonised rendering the stone black. Stones could even be created artificially; Pliny tells us that sardonyx could be manufactured so convincingly by sticking three gems together that the artifice could not be detected.