COMBINING.--Many kinds of papers, as photo-mounts, double-thick covers and cardboards, are made by pasting two or more thicknesses together. This was formerly done in the sheet, but most of the pasting is now effected in the web. The papers are run over a paste roll, combined, and passed either through a drying chamber or over a battery of driers like those of the paper machine. The pasted paper is lastly made into rolls and taken to the finishing room to be sheeted. COATED PAPERS.--Coated papers are made by covering the surface of ordinary paper with a veneer of clay, mixed with some adhesive, as casein or glue, and suitably colored. The process is done from the roll; the paper first goes through the machine where the liquid coating is brushed onto the surface, passing directly in automatically formed festoons through a long, heated room to dry, and finally is rewound. The rolls are then taken to the supercalender room and the paper is given the desired finish. Dull-finish coated papers require a special kind of coating and receive very light calendering after being coated. High-finished coated papers of the best grades are double-coated and run several times through the calenders. Another method of producing a high finish is known as “flinting.” In this process the paper is mechanically polished by smooth flint stones and gains a very high luster. Such papers are most widely used as box covering. A similar effect is obtained by friction calenders, which consist of two chilled iron rolls with an intermediate roll of hard paper. The top roll rotates at a higher speed than the others. [Illustration: COATING ROOM, APPLETON COATED PAPER CO. This view of the “wet end” of the coating machines shows the rolls going through the coating process, the web of paper traveling along the drying racks appears in the background.] The coating may be dyed to any color desired, so that coated and glazed papers are obtainable in a wide variety of shades. [Illustration: FINISHING-ROOM, CRANE & CO. The machine on the right is a plater.] GUMMED PAPERS.--Gummed papers are made by passing the web through a machine, which coats it with glue, after which it passes over drying apparatus and is wound into rolls ready for finishing. Gummed paper for labels is usually finished in sheets, while for sealing tape and box stays it is ordinarily made up into rolls. WAXED PAPERS.--Waxed papers are made by applying a coating of parrafin. This renders the stock water proof, and it is used largely as a wrapper for food products. GLASSINE PAPER.--By a special treatment in the beaters and jordans cellulose fiber is so treated as to become hydrated. This hydration makes the paper produced grease proof, and by heavy supercalendering the character of the sheet is again greatly altered, it becoming almost perfectly transparent. In this state it makes a most attractive and hygiene wrapper. CHAPTER EIGHT THE PHYSICAL AND CHEMICAL ASPECTS OF PAPER