The art of cameo engraving can be traced as far back as the second and first centuries B.C., to the ancient Greco-Roman empires, where cameos enjoyed a golden age. The decline of the Roman Empire, however, brought with it a period of dormancy for cameo development.
It was not until the Fifteenth Century, during the Renaissance, that cameos resurfaced as an art form and medium for jewelry. The Medici family of Florence, great patrons of the arts, is credited with restoring cameos as jewelry. At about the same time, a very high quality agate mine was discovered in southern Germany. This region soon became the center of cameo technology and by by the beginning of the 19th century possessed the most important agate deposits in the world.
Over the past one hundred years, this area pioneered, and is largely responsible for developing and refining, the techniques used to carve and color today's cameos. The once rich deposits of these mines have been exhausted and the world is now dependent on South America for its supply of high quality layered agate material for cameo carving.
Ultrasonically Carved Agate Cameos
The most well known place for agate cameos is Ider Oberstein, Germany. Some are still carved by hand, but the majority are now being carved ultrasonically. The machine carved cameos are then finished by hand, giving them a polished and sometimes a more sculpted look.
Ultrasonically carved cameos still have to start with a skilled artist creating an original, hand-carved agate cameo. The finished cameo then serves as a model for steel dies that are created using laser carving. The steel dies are then used to produce copper cutting tips, and the original cameo can now be reproduced ultrasonically.
Ultrasonic carving is done in liquid, using a template and vibrations to create the image. (This is different than laser carving, which uses a beam of light.) Ultrasonically carved cameos produce great detail, truly capturing the artist’s original work. Being machine produced, the image is likely to be used many times, but the quality from piece to piece remains the same.
Most agate material for cameos comes from Brazil. Very little of what is mined is suitable for the cameo trade. The natural agate used for cameos is layered in shades of gray color, ranging from a milky white to a dark gray. A layer of black agate with a white upper layer is called onyx. A layer of brown with a white upper layer is called sard-onyx. A layer of red with a white upper layer is called cornelian-onyx.
The cameo rough material is cut from agate with even parallel layers, slicing it so that there is a lighter layer above a darker one. The darker layer is softer and accepts dye, while the lighter upper layer is harder and does not accept the dye, remaining white or milky in appearance. (I have also read accounts that say the dye is chemically drawn out of the upper layer, to create the white layer.) The upper layer is then carved, exposing the darker layer underneath.