Cameo
2 of the 7 encyclopedias on this shelf carry an entry for Cameo. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a term applied to gems of different colors sculptured in relief. The art of engraving on gems boasts of high antiquity, having been practiced with various degrees of success by the Egyptians, Greeks, and Romans. It was revived in Italy in the 15th century, and is even at the present day cultivated with considerable success. The cameos of the ancients were usually confined to the agate, onyx, and sard, which, on account of the variety of their strata, were better suited to display the artist's talents; but they were also also occasionally occasior found exeand even cuted on opal, beryl, or emerald, emerald, on a sort of factitious stone, the the Vitrum obsidianum of Pliny, distinguished by the One moderns as the antique paste. of the most famous cameos is the onyx at present in Paris called the " "Apotheosis of Augustus." It is 1 foot in height, and 10 inches in width.
Aiton's Encyclopedia (1910)
a gem cut away so that the figure stands out in relief. It is the opposite in this respect to the intaglio in which the figure is a depression. If a cameo be pressed against wax it forms an intaglio, and, conversely, an intaglio pressed on wax forms a cameo impression. Cameo cutting is believed to have been practiced by the ancient Babylonians and Phoenicians. A cameo in an English collection, called the Cupid and Psyche, is believed to have been cut by a Greek not long after the death of Alexander the Great. The material most frequently used is the onyx and various kinds of shell. Artificial cameos are made of glass and other material. Florence, Italy, is celebrated for cameos and intaglio cutting.