Wall papers may be divided into 3 classes: - (1) "Common" or "pulp" papers, in which the ground is the natural colour of the paper as first made, the pattern being printed upon it.

(2) "Satin" papers, of which either the whole ground, or the pattern, or both, are of a polished lustre, having somewhat the appearance of satin. They are made by painting the paper over with the required colour, mixed with Spanish white, etc, after which it is polished with a burnisher. Or the colour is mixed with plaster of Paris, laid on, sprinkled with powdered French chalk, and then rubbed over with a hard brush to give the appearance of satin. Satin papers are very susceptible to damp, even from the paste used in hanging them; they require to be hung with care, on dry walls, and should be protected by a lining paper. When once hung, if thoroughly dry, they can be kept clean for a long time, as the smooth surface of the paper prevents dust and dirt from adhering to it.

(3) Flock papers, the design on which is formed by the adhesion of flock sheared off from the surface of woollen cloth. The pattern is first printed on the paper in size, next in varnish, the flock is then thickly sprinkled on, and adheres to the varnish, thus forming the pattern.

The pattern on the best papers is printed from wooden blocks. The position of each block is guided by 4 pins in its corners, and a separate block is required for each colour. Wall papers are printed also in large quantities, and very cheaply, by machinery, the patterns being engraved on metallic rollers, one for each colour required, and printed on continuous bands of paper several 100 yd. long. Machine-printed papers are inferior to those printed by hand; the colours of the former often wear off from not being properly set. Some of the common grained, marbled, and granite papers are roughly coloured by hand, and elaborate papers of the highest class are painted by artists.

"Pulp" papers can easily be recognized, as the back is of the same colour as the ground of the front. Hand-printed papers can be distinguished from machine-printed, as the former retain the marks of the pins used as guides for the position of the wood blocks.

Wall papers are sold by the "piece," except in the case of borders, which are sold by the yd., or 12 yd. run. The prices vary according to the description and quality of the paper, and the nature of the pattern, extra being charged for every additional colour. The introduction of gold or silver in the pattern also enhances the price considerably, in proportion to the amount used. Down each side of the paper is a blank margin about 1/2 in. wide. In hanging good papers, both these margins are cut off, and the adjacent pieces are placed edge to edge. In common papers, however, only one margin is cut off, and the cut edge of one piece of paper overlaps the margin of the next. In English papers, each "piece" is 12 yd. long and 21 in. wide; it therefore contains 7 sq. yd. After the margins are removed, the paper is 20 in. wide. Each yard in length of the paper then contains 36 X 20 in. = 5 ft. super., and each piece 12 x 5 = 60 ft. super. The number of pieces of paper required for a room is therefore equal to the number of super, ft. to be covered divided by 60. An allowance of 1/6-1/10 must be made for waste: more for good papers and large patterns than for common papers and small patterns. French papers are made in "pieces" containing 4 1/2 sq. yd.

The length and breadth of a piece vary considerably, according to quality, but they often run about 9 yd. long and 18 in. wide. Borders are sold in pieces containing 12 yd., technically known as " dozens." Lining paper is common uncoloured paper placed under the better classes of paper, in order to protect them against damp and stains from the wall below, and to obtain a smoother surface to work upon.

The colouring pigments used for wall papers are as a rule harmless; some of the white grounds contain, however, a proportion of white-lead, and in some red papers arsenic is used to fix the dye. Papers containing green are as a rule very objectionable, because they are often coloured with pigments containing arsenic, mercury, copper, copper arsenite (Scheele's green), and other deleterious substances. These fly off in the form of dust, and may poison the occupants of the room in which the paper is hung.

Damp walls should be covered with a thin sheet of some waterproof material before the wall paper is hung. Thin sheet lead, tinfoil, indiarubber, guttapercha, and thick brown paper have all been used for this purpose, the metals being the bust but most expensive. The foil is made so thin that it may be fastened to the wall with paste.

For hanging paper on damp walls the Germans coat a lining paper on one side with a solution of shellac spirit, of somewhat greater consistency than the ordinary " French polish," and then hang it with the side thus treated to the damp wall. The paper-hanging is then performed in the usual manner with paste. Any other resin that is equally soluble in spirits may be used in place of the shellac.

Wall papers (except the most delicate) may be finished with good copal varnish over 2 coats of size, or they may bo bought ready varnished. Flock papers may be painted (after well sizing) when they become shabby. In some cases they have a roller covered with wet paint passed over them, so that the raised pattern only receives the paint. Washable paperhangings, made by Wilkinson and Son, of London, are said to become as hard as stone when hung, to withstand washing, and to be non-absorbent of the contagion of infectious disorders. Such papers would of course be better than those of the ordinary description for a sick-room. The walls of hospital wards, however, are generally rendered in cement, and brought to a highly polished non-absorbent surface, thus avoiding the use of paper altogether.

Wall papers are intended chiefly for ornament; they relieve the bareness of the walls, and give the room a bright cheerful appearance. A plain white paper may sometimes be applied with advantage to ceilings, especially where, from want of stiffness in the floor above, or from some defect in the plastering, the ceiling is inclined to crack.