QUARTZ. - Pure silex, occurs both crystalline and amorphous and is polished after the mode described for Carnelian. The reader is also referred to the article Crystal, by which name Quartz is very commonly known in the arts.
RAGSTONE. - See Hone Slates, article 1.
RED STUFF. - A name applied by watchmakers to some kinds of crocus, or the oxide of iron, the manufacture of which is described under the head Oxide of Iron.
RHODIUM, which is an extremely hard metal, is generally figured and ground on an iron lap, into the surface of which fragments of diamond have been hammered. As a temporary expedient rhodium may be polished on a brass lap with oilstone powder and oil, using a high velocity.
ROCK CRYSTAL. - See Crystal.
ROTTENSTONE is a variety of Tripoli, almost peculiar to England, and proves a most valuable material for giving polish and lustre to a great variety of articles, as silver, the metals, glass, and in the hands of the lapidary even to the hardest stones. It is found in considerable quantities both in Derbyshire and South Wales.
ROUGE. - See Oxide of Iron, articles 1 and 4.
SARD. - A variety of Chalcedony that is wrought by the lapidary like Carnelian.
SARDONYX. - Idem.
SATIN STONE or fibrous gypsum is treated much the same as Alabaster, but requires additional tenderness. See Alabaster, article 3, also vol. 1, page 164.
SAW DUST is used by jewellers, brass finishers, and others, in drying the metals after they have been pickled and washed. The saw dust of boxwood is preferred for jewellery on account of its freedom from turpentine or resinous matter; the saw dust of beech wood is next in estimation.
SCAGLIOLA, Keene's Cement, and other factitious marbles, are treated nearly the same as marble; but they generally require less labour because they are accurately moulded into form, and are somewhat softer than the generality of marbles; but when the materials are of unequal hardness the difficulty of the polishing is increased, from the softer parts wearing down too rapidly, and leaving the surface irregular.
SERPENTINE, when in large pieces, is treated like marble; when the serpentine is in small pieces, that are recent and soft, the lapidary employs much the same mode that he would in grinding and polishing Alabaster, (see article 3,) or the routine for Carnelian, when from exposure to the atmosphere the serpentine has attained its greatest degree of hardness.
SILEX is the basis of tripoli, sandstones, sand and some other polishing powders. It constitutes from about 65 to 98 per cent. of these substances, and is the fourth or fifth of the polishing materials in the order of hardness, - silex being preceded by carbon and alumina, and probably by the oxides of iron and tin. See page 1029 of this volume.
See also Crystal and Quartz.