Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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degreasing

The removal of excess natural grease from skins, mainly sheepskins, but also other skins which may happen to be particularly greasy. Degreasing may be necessary because excessive amounts of grease in a skin may interfere with uniform penetration of tannins or dyes, cause difficulties in finishing processes, and/or show as dark, greasy patches in the finished leather.

A typical method of degreasing is with the use of paraffin. The well-drained, but still damp, pickled skins are drummed vigorously with about half their weight of paraffin oil (or kerosine, water, and salt), which loosens the grease. To aid penetration of the paraffin into the wet skin, a small amount of a wetting agent, e.g., 5% of a non-ionic wetting agent, may be added. The loosening of the grease is hastened by heating the paraffin beforehand. At the conclusion of the paraffin drumming, the now greasy paraffin is drained off. A considerable amount of greasy paraffin may still be held in the skins and can be removed by squeezing processes, such as SETTING OUT , or by centrifuging. However, as these processes are difficult and expensive to carry out, it is more usual to wash the skins in a 5% salt solution. Salt must be used as water alone would result in acid swelling. (306 , 363 )




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