Page:Paper and Its Uses.djvu/59

Rh Plate papers are fine papers, soft-sized, lightly rolled, usually having one side only with a smooth finish. Thick plate papers are made by rolling two or more webs of wet paper together, and finishing as usual. The softness of the paper enables it to take all the ink from the finest lines of the steel or copper plates printed upon the surface.

Poster paper for lithographic or letterpress printing is made with a rough back to enable pasting to hoardings to take place more easily. These papers are made on the single cylinder machine, and, having only one side glazed—the printing side—are known as M.G. poster papers.

Imitation art papers are distinctly between super-calendered printings and art papers in printing quality, but they lack strength, owing to the method of their manufacture. Art paper has a mineral coating, while imitation art has a large percentage (about 25 per cent.) of china clay mixed with the pulp. China clay, having no cohesion, does not assist in felting the paper in any way, but tends to weaken its resistance to wear. That weakness or tenderness is one feature of imitation art papers. After leaving the paper machine the paper is super-calendered, receiving a water finish, that is, the paper is just wetted on the surface immediately before entering the rolls of the calender. The loading is thus brought to the surface, and a very smooth level sheet is produced, only a little inferior, as a printing surface, to art paper. Being opaque, suitable for half-tone printing, and of good appearance, imitation art is used largely for illustrated magazine work, and serves the purpose well, but it should be remembered that the large proportion of mineral matter renders the paper liable to disintegration from frequent handling.