Until the 14th century, almost all the gems were cut en cabochon —that is, smoothly rounded, as carbuncles and agates are still— or else in the form of beads drilled from both sides for suspension or attachment, the two perforations often meeting but imper fectly. These latter may be of Asiatic origin, brought into Europe by commerce during the Crusades. Some of the finest gems in the Austrian, Russian and German crowns are stones of this per forated or bead type. An approach, or transition, to the modern facetting is seen in a style of cutting often used for rock-crystal in the loth and iith centuries : an oval cabochon was polished flat, and the sides of the dome were also trimmed flat, with a rounded back, and the upper side with a ridge in the centre, tapering off to the girdle of the stone below.
The plane facetted cutting is altogether modern; and hence the pictures which represent the breastplate of the ancient Jewish high-priest as set with facetted stones are wholly imaginary and probably incorrect, as we have no exact knowledge of the forms of the gems. The Orientals polish gems in all sorts of irregular, rounded shapes, according to the form of the piece as found, and with the one object of preserving as much of its original size and colour as possible. The greatest ingenuity is used to make a speck of colour, as in a sapphire, tone up an entire gem, by cutting it so that there is a point of high colour at the lower side of the gem.
In later times a few facets are sometimes cut upon a generally rounded stone. The cabochon method is still used for opaque, translucent and some transparent stones, as opal, carbuncle, etc.; for most transparent gems the facetted cutting is almost always employed, on account of its fine effect in producing brilliancy, by reflection or refraction of light from the under side of the gem. Occasionally the ancients used natural crystals with polished faces, or perhaps at times polished these to some extent artificially.
Numerous facets, geometrically disposed to bring out the beauty of light and colour to the best advantage, are now cut.
This is done at the sacrifice of material, often to the extent of half the stone or even more—the opposite of the Oriental idea. There are various forms of such cutting, but four are specially used: the brilliant, the rose, the baguette and the table-cut. The last, generally made from cleavage pieces, usually square or ob long, with a single facet edge on each side, and occasionally four or more facets on the lower side of the stone, is used chiefly for emeralds, rubies and sapphires; the two former for diamonds in particular. The brilliant is essentially a low, double cone, its top truncated to form a large flat eight-sided face called the table, and its basal apex also truncated by a very small face known as the culette or cullet. The upper and lower slopes are cut into a series of triangular facets, 32 above the girdle, in four rows of eight, and 24 below, in three rows, making 56 facets in all. The rose form is used for diamonds not thick enough to cut as' brilliants; it is flat below and has 12 to 24, or sometimes 32, triangular facets above, in three rows, meeting in a point. Stones thus cut are also known as "roses couronnees"; others with fewer facets. twelve or even six, are called "roses d'Anvers," and are a specialty at Antwerp. Baguettes are flat stones with four, eight, or more facets and a simple top.
Modern gem cutting and engraving are done by means of the lathe, which can be made to revolve with extreme rapidity, carrying a point or small disk of soft iron, with diamond-dust and oil. The disks vary in diameter from that of a pin-head to a quarter of an inch. Better than the lathe, also, is the S. S. White dental engine, which the present writer was the first to suggest for this use. The flexibility and sensitiveness of this machine enable it to respond to the touch of the artist and to impart a personal quality to his work not possible with the mechanical action of the lathe, and more like the hand-work with the sapphire point.