Although many of the gem-stones have been endowed by nature with brilliant lustrous faces and display scintillating reflections from their surfaces, yet their form is never such as to reveal to full perfection the optical qualities upon which their charm depends. Moreover, the natural faces are seldom perfect; as a rule the stones are broken either through some convulsion of the earth’s crust or in course of extraction from the matrix in which they have lain, or they are roughened by attrition against matter of greater hardness, or worn by the prolonged action of water, or etched by solvents. Beautiful octahedra of diamond or spinel have been mounted without further embellishment, but even their appearance might have been much improved at the lapidary’s hands. By far the oldest of the existing styles of cutting is the rounded shape known as cabochon, a French word derived from the Latin _cabo_, a head. In the days of the Roman Empire the softer stones were often treated in this manner; such stones were supposed to be beneficial to those suffering from short-sightedness, the reason no doubt being that transparent stones when cut as a double cabochon formed a convex lens. According to Pliny, Nero had an emerald thus cut, through which he was accustomed to view the gladiatorial shows. This style of cutting was long a favourite for coloured stones, such as emerald, ruby, sapphire, and garnet, but has been abandoned in modern practice except for opaque, semi-opaque, and imperfect stones. The crimson garnet, which was at one time known by the name carbuncle, was so systematically thus cut that the word has come to signify a red garnet of this form. It was a popular brooch-stone with our grandmothers, but is no longer in vogue. The East still retains a taste for stones cut in the form of beads and drilled through the centre; the beads are threaded together, and worn as necklaces. The native lapidaries often improve the colour of pale emeralds by lining the hole with green paint. [Illustration: _PLATE V_ JEWELLERY DESIGNS] [Illustration: FIG. 40.—Double (Convex) Cabochon.] [Illustration: FIG. 41.—Simple Cabochon.]