It was only towards the end of this period that more unkindly stones began to be used, such as jasper and the different kinds of agate, onyx, chalcedony, rock-crystal, garnets, &c. The employment of such materials implies that of the characteristic processes of gem-cutting, whose peculiarity consists in the substitution of friction for cutting, in the supercession of a pointed or edged tool by a powder taken from a substance harder, or at least as hard, as the one to be operated upon. “The modern engraver upon precious stones,” says M. Soldi, “sets about his work in this fashion. He begins by building up a wax model of his proposed design upon slate. He then takes the stone to be engraved, and fixes it in the end of a small wooden staff. This done he makes use, for the actual engraving, of a kind of lathe, consisting of a small steel wheel which is set in motion by a large cast-iron flywheel turned by the foot. To the little wheel are attached small tools of soft iron, some ending in a rounded button, others in a cutting edge. The craftsman holds the staff with the stone in his left hand; he brings it into contact with the instrument in the lathe, while, from time to time, he drops a mixture of olive oil and diamond dust upon it with his right hand; with the help of this powder the instrument grinds out all the required hollows one after the other.”[303] [Illustration: FIG. 138.--Engraved shell. British Museum.] The first engravers who attacked precious stones had no diamond dust. They supplied its place with emery powder, which was to be found in unlimited quantities in the islands of the Archipelago, whence it was imported by the Phœnicians at a very early date. Moreover there was nothing to prevent them crushing the precious stones belonging to the class called _corundum_, such as sapphires, rubies, amethysts, emeralds, and the oriental topaz. No doubt the lathe or wheel was a comparatively late invention. M. Soldi thinks it hardly came into use in Mesopotamia till about the eighth century B.C. Before that the continuous rotary movement that was so necessary for the satisfactory conduct of the operation was obtained by other means. According to M. Soldi they must have employed for many centuries a hand-drill turned by a bow, like that of a modern centre-bit or wimble.[304] [Illustration: FIG. 139.--Chalcedony cylinder. British Museum.] [Illustration: FIG. 140.--Cylinder of black jasper. British Museum.]