Page:Paper and Its Uses.djvu/95

Rh to be varnished may be printed on litho. paper, which is sized and varnished after printing, or a varnishable paper, one that is hard-sized and finished in the manufacture, may be used, varnish being applied without previous sizing, as soon as the ink is dry. A thick litho. paper is seldom as strong as a thinner one, and with the greater thickness goes more liability for the surface to pluck.

The thinnest and commonest papers should not be chosen for set-off or interleaving sheets. Although many papers, when printed, absorb the ink and hasten the drying, it must be remembered that printer's ink, like paint, dries by oxidation, and the more freely air can reach the film of ink the quicker and more thorough will be the drying. A rough surfaced paper is most suitable for interleaving, as it will not stick to the printed matter, and it allows air to penetrate between the sheets. For interleaving colour work in which bronze is used at all, a paper of fair quality must be used, for common papers may contain chemical residues which will affect the brightness of the bronzed work. Paper equal to 24 Ib. demy will serve admirably, and may be used repeatedly.

Proofs should be printed upon the paper which is to be used for the job, if that is possible. Galley proofs require a paper which is moderately sized, not too soft, or corrections made in ink may be undecipherable from the spreading of the ink.

It is not difficult to distinguish between the right and wrong sides of paper, and little excuse can be made for the printer who uses the wrong side. Flat papers are usually packed with the right side uppermost; if the paper is folded, the right side is utwards. There is a slight diversity of practice among paper-makers, but the general rule is as stated. In a very