In order to prevent common ink from running upon paper, size is introduced at a certain stage of the manufacture; but printing-ink being oily instead of watery, and, moreover, of greater consistence than common ink, is not so liable to run. Hence, for certain printing-papers, the sizing is done in the beating-engine towards the close of the operation. The size consists of finely pounded alum mixed with oil, about a pint and a half of the mixture being thrown into the engine at intervals during the last half hour of the beating. The blue is produced by smalt, or artificial ultramarine. PAPER-MAKING BY HAND. When the stuff is properly prepared, it is run out by the pipes _o o'_, Fig. 4, into the _stuff-chest_, where the different kinds are mixed preparatory to moulding. From this chest it is transferred to vats or tubs, each about five feet in diameter and two and a half feet deep, provided at top with planks inclosed inwards to prevent the stuff from running over during the moulding. Across these planks is a board pierced with holes at one extremity, for supporting the mould. The stuff in the vat is kept at the proper temperature by a small grate placed in a hole lined with copper, at the side of the vat. The fuel is charcoal or coke, or the fire is entirely confined to the other side of the wall, a hole through it being made into the side of the vat. In this way smoke is prevented. The paper is made into sheets by means of the _mould_ and _deckle_, Figs. 6, 7. The mould is a square frame, or shallow box of mahogany, covered at the top with wire-cloth; it is an inch or an inch and a half wider than the sheet of paper intended to be made upon it. The wire-cloth of the mould varies in fineness with that of the paper and the nature of the stuff; it consists of a number of parallel wires stretched across a frame very near together, and tied fast through holes in the sides; a few other stronger wires are also placed across at right angles to the former; they are a considerable distance apart, and they are bound to the small wires at the points of intersection by means of fine wire. In several kinds of writing-paper the marks of the wires are evident from the paper being thinner in the parts where the pulp touched the wires. In what is called _wove_ paper, there are no marks of the wires; these are avoided by weaving the wire in a loom into a wire-cloth, which is stretched over the frame of the mould, and being turned down over the sides is fastened by fine wire. The _water-mark_ in paper is produced by wires bent into the shape of the required letter or device, and sewed to the surface of the mould;--it has the effect of making the paper thinner in those places. The old makers employed water-marks of an eccentric kind. Those of Caxton and other early printers were an ox-head and star, a collared dog's head, a crown, a shield, a jug, &c. A fool's cap and bells employed as a water-mark, gave the name to _foolscap_ paper; a postman's horn, such