Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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drenching

An old method of deliming and acidifying unhaired skins, in lieu ofBATING or PICKLING , by means of immersion in a water infusion of fermented barley, sour dough, flour, or the husks of cereals. The organic acids (lactic and acetic) in the solution neutralized any remaining lime in the stock and the particles of barley, etc., exerted a cleansing action of the skins, absorbing dirt and greases, etc. The cleansing action was very effective because the enzymes produced by the bacterial cells not only broke down the carbohydrates in the plant materials to produce acids but also digested the mucopolysaccharides of the ground substance.

Drenching was often difficult to control, as the enzymes did not restrict their attack to the carbohydrates either in the solution or the skins, but often degraded the fibers of the dermal network as well. In addition, too much acid swelling was produced with resulting impairment of the skin structure and, therefore, of the quality of the leather produced.

When drenching is used today, as in certain vegetable tannages calling for specific acid conditioning during the early stages of tanning, weak solutions of organic acids, such as lactic, acetic and formic, are used in lieu of fermented cereal solutions.

Because of the gas bubbles of carbon dioxide produced by fermentation, which caused the skins to rise to the surface of the paddle, the process was also called "raising." (291 , 363 )




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