paper, and as there are several cylinders, each in its own vat, producing paper in the same way, the several webs are brought together, rolled, dried, and reeled. In the case of a duplex board the pulp may be the same colour, or of two different shades. In triplex boards, the outsides are frequently thin and different in colour, compared with the middle sheet. Cylinder machines with as many as seven vats are in use, and forty to fifty drying cylinders are necessary to complete the extraction of the water.
Pasteboards are made up from middles and pastings. These are obtained from mills making specialities of these lines, the middles very often consisting of a moderately thick paper of poor quality, but the outsides are of fairly fine paper. The papers are not glazed, but after pasting together the web is thoroughly rolled and the surface obtained by subsequent calendering. Bristol boards are made from the finest materials, all-rag, tub-sized papers, the same paper throughout pasted, pressed and surfaced by hot-pressing. Other boards supplied under this title are made of good drawing paper for outsides, and cartridge for middles. The best boards are made by hand, and take considerable time and care in manufacture.
Millboards, the thicker kinds of box boards, slate boards, leather boards, portmanteau boards, and carriage panels are made on a special board machine. For leather boards a large percentage of pulped leather is sometimes employed. For the other kinds a large variety of materials finds its way to the machine, but it is waste in the form of flax, ropes, coarse rags for the best qualities, and for the lower grades waste papers of all kinds. The stronger materials are boiled and beaten, bleaching being unnecessary. Waste papers are simply steamed and pulped. All materials are strained, diluted
