Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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tawing ( tawed "leather" )

An ancient process of treating prepared hide or skin (usually pigskin or goatskin) with aluminum salts and (usually) other materials, such as egg yolk, flour, salt, etc. A skin may actually be tawed simply by immersing it in an aqueous solution of potash alum at a temperature between 20 and 30° C; however, salt is usually included in the alum solution because it improves the substance (thickness) of the final product. After treatment the skin is dried in air (crusted) and held in this condition for several weeks to allow the development of stabilization or "aging" effects. Tawed skins also undergo STAKING to impart of soft, flexible handle. Apart from this soft, warm handle, the tawed skins have a high degree of stretch. Handle and stretch may also be improved by the addition of egg yolk and flour to the basic alum and salt solution. A tawed skin is usually white in color but may yellow slightly with age.

Tawing does not actually produce a skin that is stable in the wet condition, i.e., imputrescible in the wet state, and therefore cannot accurately be described as having been tanned; consequently, in a strict sense, a tawed skin is not leather. (61 , 237 , 291 )

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