Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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1. The process of treating raw hides and skins with water. The restoration of moisture lost during curing and storage, as well as the removal of extraneous matter are of prime importance in converting raw stock into leather. The restoration of moisture is essential because: 1) the stock may otherwise be physically damaged by the action of washing under agitation, and flexing during green or lime fleshing; 2) sufficient moisture within the stock is necessary for solution and elimination of salts and globular proteins contained within the fibrous hide structure: and 3) the replenished water serves as a diluent as well as a vehicle for penetration into the fibrous structure of the astringent chemicals employed to effect hair loosening, plumping. and required alkaline action. Removal of extraneous organic and inorganic matter, except epidermis and flesh, by soak-washing is essential because: 1) solid matter in excessive amounts can result in both stock and machine damage during fleshing a nd unhairing; 2) manure and urine are ideal foods for bacterial growth during soaking. (Such matter, along with certain salts in the soaks, can result in discoloration and stains on the stock that cannot subsequently be removed): 3) the cementing effect of globular proteins upon dried tanned fibers reduces fiber mobility necessary for softness and good handle in the final leather; 4) curing salts transferred to the lime liquors affect the alkaline plumping action, reduce the rate of unhairing, and cause a contraction of the grain surface of the stock; and 5) the presence of extraneous matter presents a false and variable hide substance weight in determining the amounts of materials required for liming.

Because of many variable conditions. the time and temperature of soaking varies considerably according to the kind of stock being treated. Generally, few soaking aids are used in soaking cured and brined stock unless a considerable number of a given lot have been stored under exceptionally dry and warm conditions. In such cases. either sodium sulfide (63%) or sodium hydroxide may be used to the extent of 1.0 to 0.S pound respectively per 100 gallons of water. These chemicals are frequently employed in the soaking of dry stock. Excessive amounts will cause a high grain in the leather.

2. The process of wetting the grain side of a leather with water and the flesh side with paste to improve the pliability of the leather preparatory to covering. (161 , 248 , 291 , 298 , 306 , 363 )

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