Sand-paper is made of paper with a coating of finely-ground flint, glass, or quartz glued on to it. The grains on the same paper are always of the same size, and, according to the finer or coarser quality, the paper is numbered from 0 to rough 2.
Sand-pajyer made of flint and of glass.
[Sand-paper made of flint is generally used in Sweden. In England, glass-paper is considered the best. - Trs.]
When in use, the sand-paper should be torn off in pieces of convenient size, and a bit laid on the plane surface of a piece of cork or wood, 3/4-inch thick, and of a good size to be held in the hands. If a sufficiently thick piece of cork cannot be obtained, a thin piece should be glued on a piece of wood, or, failing cork, a piece of card-board will answer the purpose. This serves the purpose of a soft rubber (wood alone being too hard), and gives the necessary support to the sand-paper, which, used in this way, acts much in the same manner as the file, and may be considered to all intents and purposes as a tool.
Sand-paper really a tool.
Sand-paper may be used without a rubber only in the case of concave or convex surfaces, where there are no sharp edges. Care must be taken in finishing off not to work the paper in the direction of the fibres, but either at right angles or obliquely to it, in order to produce a smooth surface. Just at the last, the paper may be passed once or twice in the same line as the fibres, to remove any ridges or marks which may have been produced. For similar reasons, the paper last used should be finer than that first employed, in order to secure a perfectly smooth surface.
Sand-paper should never be used to form or smooth up the surface of objects. The knife, the file, the smoothing-plane, the scraper, etc. are the proper tools for this purpose. Sandpaper should be used only in finishing off, and when the use of the smoothing-plane is understood, it is not much needed for plane surfaces. In the case of objects with curved surfaces, on the other hand, it is almost indispensable.
Finishing off with sand-paper should never be done in a thoughtless, mechanical way. To attain a satisfactory result the greatest attention is requisite.
Sand-paper should be used sparingly.