Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

drying

Drying is employed principally in situations where insufficient salt is available for WET-SALTING , or where the cost of salt is too high to be economical.

As bacteria must have a certain amount of moisture or free water if they are to attack a hide or skin, putrefaction can be effectively stopped or prevented by removal of the water to the point where the skin contains only 10 to 14% moisture. At this point the activity of the bacteria ceases, and some types are killed, while the others dry up into spore form, in which they can remain for long periods or until there is enough water for them to again become active.

Curing by drying requires considerable care, especially with thick hides, because: 1) if drying is too slow, as may be the case in relatively wet, cold climates, putrefaction may occur before the moisture content is low enough to inhibit bacteria; and 2) if drying is too rapid and the temperature is too high, part of the wet skin will begin to gelatinize, which will show as holes in the hide when it is subsequently brought back to its normal moisture content. Too rapid drying also makes the hide hard and brittle and prevents drying of the inner layers.

Drying as a means of curing is usually practiced in countries with hot, dry climates. The skins may be: 1) ground dried—by simply spreading them out on the ground, sometimes on a bed of twigs or stones. This is potentially dangerous because of poor ventilation on the ground side and too high a temperature on the exposed side, plus contamination with dirt; 2) sun dried—in which the skins are hung or laid over poles or wires in the sun. This method affords better ventilation and quicker drying, but may result in heat damage or pole or wire marks, showing as hard creases down the skin; 3) frame dried—in which the skins are loosely stretched out on frames, which are arranged so that they do not receive the direct rays of the mid-day sun. This results in less danger of heat damage and a superior, flatter shape; however, a skin shrinks on drying, and if it is stretched too tightly on the frame, overstraining may cause thinness and weakness; and 4) shade dried—where the skins are dried in an open-sided, covered shed, designed to avoid the direct heat of the sun but to allow good ventilation. See also: DRY-SALTING . 2. The process of allowing books to be "set" after each operation, involving the use of adhesives and/or seasoning a book in a press after casing-in or covering. (256 , 291 , 306 , 363 )