Gems and their creation

A gem is a precious or semiprecious stone that has been cut, polished, engraved, or otherwise altered to be used as a personal insignia for making sealings or as decoration. Often imported from afar, ancient gems were truly exotic, and their bright colors and luminescence added to their value.

Semiprecious gems have long been carved with decorative and figural designs. Opaque and translucent quartzes and chalcedonies, popularly known as cornelian (or carnelian), sard, jasper, onyx, and sardonyx, come in a variety of colors. Their hues can also be artificially enhanced through a variety of methods. Banded agate, shown above, is another type of quartz that can be opaque or translucent. Other quartz gemstones, such as amethyst, shown below, and rock crystal, can range from translucent to clear.

The deep color of the translucent amethyst used for the Portrait of Aurelian (above right) and the skillful engraving of the image suggest that an imperial workshop created this gem. It may have been a gift from the emperor, a sign of imperial favor.

Pure black onyx (above left), an opaque quartz gemstone, is common and perhaps the most famous variety, but it is not as common as onyx with banded colors that range from white to tan, brown, and darker colors. The banded onyx gem (above right) depicts cupids, or amores, in a scene could be a metaphor for their many conquests in affairs of the heart.

Carvers also engraved more precious gemstones including ruby, as well as lapis lazuli and garnet (both shown above). First mined 6,000 years ago in Afghanistan, lapis lazuli was transported to Egypt and later to Europe where it was set in jewelry or crushed for use as an expensive paint pigment. Varying from translucent to opaque, garnet species are found in many colors, including red, used by the ancients, as well as orange, yellow, green, blue, purple, brown, black, pink, and they can also be colorless.

Craftsmen in ancient Mesopotamia, Egypt, and the Bronze Age Aegean, as well as later in Greece, Etruria, and Rome, used hand-powered tools to engrave gems.

To create intaglios (the modern word from the Italian intagliare, “to cut into”), they used rotating cutting tools to engrave images into gemstone blanks. Intaglio is a technique of creating a design that is sunken into the surface. An intaglio gem (see below) could be used to make relief impressions when pressed into wax or clay.

Around 250 B.C., a new carving technique developed. By cutting away the stone surrounding a figure, artisans formed small relief images known as cameos (see below). The different hues of banded stones were exploited to create the illusion of depth with multi-colored compositions, so that the main design or figure stood out in one color against the background of another color.

Although intaglios are concave and cameos are convex, the ancient methods used to produce both were similar and, apart from the modern use of power tools, were much the same as those employed today. The video The art of gem carving provides a visual demonstration of the gem carving process.

From a carefully selected chunk of rough stone, considering color and density, the gemstone is separated by percussion (striking a solid object against another) and flaking. The stone is then further shaped using a wheel or grinder. Color enhancement can be performed if desired by a variety of methods, including soaking the gem in a solution of iron and/or heating it.

Ancient gem carvers would work, or engrave, stones using various hand-powered drills, which were made to rotate with the help of a wheel or some other device such as a bow. When drawn quickly back and forth, the bow drill could produce a rotating movement similar to that of a wheel. Cutters of different shapes, such as finely shaped drills and cones, were made of copper, bronze, iron, or softer material, such as wood or even reed.

The cutting tool was dipped in a slurry, which is a mixture of oil and abrasive powder (volcanic corundum in antiquity, diamond dust today). It is the mixture of oil and powder carried by the tools—not the tools themselves—that cuts a gem. This method of engraving has been used by carvers since antiquity.