[Illustration: The final step in preparing a gemstone from rough is the applying of a high polish by pressing the stone against a rotating disk that has an extremely fine abrasive on its surface. Here, the disk is of felt, and the abrasive is tin oxide.] [Illustration: The cabochon cut gets its name from the French word “caboche,” meaning pate or knob, a reference to the rounded top of the stone. Here, from top to bottom, beginning at left, are cabochons of turquoise, agate, and petrified wood; jasper, smithsonite, and williamsite; and amazonite, petoskey stone, and carnelian. (Two-thirds actual size.)] [Illustration: These exquisite bowls, measuring 2 to 3 inches across, are part of a set of 35 carved by George Ashley of Pala, Calif., from gem materials found in the United States. Left to right: paisley agate from California, petrified wood from Arizona, black jade from Wyoming, chrysocolla from Arizona, and variscite from Utah. (One-third actual size.)] Shaping of gemstones is not limited to geometric faceting. Many stones, especially those which are opaque or which produce stars and cat’s-eyes, are cut as _cabochons_. This ancient, and probably oldest, cutting style consists merely of a raised and rounded form. When extended completely around the stone, the cabochon form results in a bead that can be drilled and strung. Many cabochons, especially those of less expensive gem materials, are now cut in large quantities to standard sizes in order to fit mass-produced gem mountings. Sculpting in gemstones is a much more intricate, nongeometric kind of shaping. Although tools differ in detail, and the gem sculptor must possess an artistic eye as well as lapidary skill, the basic processes of sawing, grinding, and polishing are the same. [Illustration: This coral carving, 11 inches tall without the stand, owes its thin, graceful, willowy shape to the skill of the artist in following the contour of a natural coral branch.] [Illustration: The contemporary sculptor Oskar III J. W. Hansen visualized and created the likeness of a spirited stallion in this 4½-inch turquoise carving, a gift of George Gilmer.] [Illustration: This world-famed crystal ball, given to the Collection as a memorial to W. R. Warner by his widow, represents another phase of the lapidary art. Cut from a block of Burmese quartz estimated to weigh 1000 pounds, this extremely valuable, flawless, colorless sphere has a diameter of 12⅝ inches and weighs 106¾ pounds.] 4 GEM SUBSTITUTES