Page:Paper and Its Uses.djvu/67

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papers and for much jobbing work, as well as for the purpose for which they were originally intended.

Covers for exercise books are usually glazed on one side only (M.G.). This should be the outside of the book, and any printing should be executed on the smooth side. "Pressings" are the papers usually employed for such purposes, a cheap cover paper obtainable in various colours, weights, and sizes.

Gummed papers are made in a variety of qualities, colours, and substances. The papers range from the thinnest printing to thick enamelled paper, and the thickness of the coating of gum is varied to meet all requirements. Many colours of paper can be procured ready gummed. To obtain a satisfactory gummed paper three things have to be studied: body paper, gum, and thickness of coating. The inherent fault of gummed papers is the tendency to curl, but the extensive manufacture of non-curling gummed papers has done much to remove this bugbear. By adopting a paper which is affected but little by atmospheric changes something is accomplished in the minimising of curling, but by an ingenious breaking of the gummed surface non-curling is secured. When the coating is dry, the paper is drawn over a steel edge to break the homogeneous film of gum into innumerable fragments. In absorbing or parting with moisture (the cause of curling) the small particles can only act as individuals instead of combining and curling. Any kind of paper can be gummed, but the thinner the paper the more effective its adhesion when used as a label. When a label, slip, or any printed matter has to cover other printed matter, the paper must be thicker and opaque enough to prevent the matter beneath from showing through.

Wrapping papers are of many kinds, of various substances and colours, and are varied, too, in surface.