Other papers are so treated chemically as to produce certain effects under the application of pressure, instead of by the action of light. Such is the transfer-paper used for transferring a design mechanically, which is prepared by coating the sheet with adhesive pigments of lampblack, vermilion, indigo, or other chemical. The carbon-paper universally used in typewriting when more than one copy of a letter or paper is desired, is paper faced with carbon or lampblack. Alternate sheets of writing and carbon paper, placed one above the other, are put into the typewriter, and the impression of the letter on the surface of one sheet serves to print three or four sheets underneath. ♦Manifold♦ Manifold writing or copying papers are made from strong unsized papers adapted to receive writing or printing, and to transfer this readily under pressure to another sheet which has been dampened. It is the common rule to-day to make permanent record of correspondence and business transactions by the use of this system of impression-copying. The manifold paper largely used by railroads is very thin, making possible a large number of copies from a single impression, thus effecting a great saving of time and labor. ♦Stencil♦ Stencil-paper is produced by giving to a sheet of fibrous paper, as fine and thin as gauze, a thick, even coating of paraffin, and from this the stencil may be prepared in two different ways. Either it may be placed in the typewriter, from which the ink-pad or ribbon has been removed, and the stencil cut by allowing the type to strike the wax sheet, or it may be placed upon a flat steel plate, the surface of which is cut into multitudinous microscopic steel points, and then written upon by a stylus, a steel pencil made especially for the purpose, which cuts the wax without tearing the gauzy body of the sheet. Copies are produced in the same manner as with other stencils, viz., by placing the blank sheet under the stencil and then passing an inked roller over the latter. Luminous paper is prepared by compounding the pulp with gelatine and phosphorescent powder. ♦Transparent paper♦ Transparent papers are made by several different methods. The usual one employed is to apply a thin coating of a solution of Canada balsam in turpentine, or a solution of castor or linseed oil in absolute alcohol, the alcohol in the latter case being permitted to evaporate, thereby rendering the paper transparent. Such paper is largely used for tracing purposes, and may be restored to its original state of opacity, with the tracings left unchanged, by removing the oil with a fresh bath of alcohol. ♦Safety♦ Safety-paper is a paper so treated or coated with chemicals that any ink-writing upon its surface cannot be erased, effaced, or removed without leaving indelible marks on the paper. As its name implies, it is used for safety in bank-checks or other commercial paper, to protect against alteration.