SKIVE. - The iron lap used by the diamond polishers in finishing the facets of diamonds for jewellery. The skive is charged with fragments of diamond powder that are burnished into its surface. - See Diamond, also page 176, vol. 1.
SLICER. - See Slitting Mill.
SLITTING MILL or the Sheer, is a very thin sheet-iron disk, the edge of which is charged with diamond powder, and lubricated with brick oil. The sheer is the circular saw of the lapidary. See the chapter on Lapidary Work.
SNAKE STONE. - See Hone Slates, article 3.
SOAP AND WATER have been proposed by Mr. Reveley, to be used on hones instead of oil, in setting razors and other fine instruments, as being more cleanly and effective.
The hone is to be wiped clean with a wet sponge, and the lump of soap also wetted, is to be rubbed on until it produces a thin lather, which is to be sponged off when the hone is laid by. - Trans. Soc. of Arts, vol. xxxix. p. 137.
SOFT WOOD. - See Wood.
SPECULAR IRON ORE. - See Oxide of Iron, articles 5 and 6.
STEATITE, especially when first raised, is a soft unctuous magnesian mineral, and is thence called soapstone, but like Potstone, and Serpentine, which it nearly resembles in its constituent parts, it becomes considerably harder by exposure to the air. Steatite when recent, may be treated by the method practised in Germany with Potstone, (which see on page 1087,) and when indurated, by the same routine that is employed for alabaster by the lapidary. Many of the Chinese idols and other figures, are carved in Steatite, which has thence been called Figure Stone. See vol. 1, page 166.
STEEL. - The parts of Machinery made in steel, are polished as described in the general article Machinery, in this Catalogue, page 1072.
SURFACES. - The principal modes of grinding plane surfaces are described in Chap. XXXIII. Section 1.
TIN is seldom polished except when in the form of tin-plate, for which purpose, rottenstone and oil, or whitening and oil may be used, dry whiting being lastly applied to remove the grease.
Works in solid tin are occasionally made by pewterers, and polished the same as that useful alloy. See Pewter.
TIN, OXIDE OF. - See Putty Powder.
TOPAZ; of the Brazilian Topazes, there are the yellow, which is best known, the blue, and the white, the latter being more commonly called the Mina Nova. The Brazilian Topazes are worked like Carnelian, the Oriental Topaz, which is in fact a yellow variety of Sapphire, is treated like other Sapphires, and is cut into facets with diamond powder and polished with rottenstone, as more fully described under the head Sapphire. The difference in hardness of the two gems is satisfactorily accounted for by their analysis, as the Brazilian Topaz contains about 50 per cent. of alumine, the Oriental about 98 per cent. of alumine; this substance being next in hardness to the diamond.