Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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bleaching

1. The process of treating pulps used in papermaking with chemicals to alter their color so that the pulp and the resulting paper will have greater brightness. Such bleaching is usually accompanied by partial removal of noncellulosic materials, e.g., LIGNIN .

2. The process of chemically treating archival materials in order to remove stains, discoloration, foxing, etc., and/or to restore brightness. Both oxidizing—i.e., chemicals which take up electrons—and reducing—i.e., chemicals which give up electrons—chemicals are used, the former much more extensively than the latter. Chemicals which are, or have been, used include CALCIUM HYPOCHLORITE ,CHLORAMINE T . , CHLORINE DIOXIDE ,FORMALDEHYDE ,HYDROGEN PEROXIDE ,POTASSIUM METABISULFITE ,

SODIUM CHLORATE ,SODIUM CHLORITE ,SODIUM HYPOCHLORITE , and SODIUM PEROXIDE . 3. The process of lightening the color of a vegetable-tanned leather by means of the removal of the oxidized tannins and insoluble matter from the outer surfaces of the skin, usually by treatment with a solution of sodium carbonate, washing, and then treatment with diluted acid. Chrome-tanned leathers are usually bleached by treating the skin with acid solutions of syntans and at times by precipitating white pigments in the grain layer of the leather to impart a bleached appearance. 4. The destructive effects of chemical agents on water colors, inks, fugitive colors, etc. 5. The generally undesirable and destructive effect of natural and artificial light on archival materials, especially cloth and leather bookbindings. (62 , 77 , 218 , 320 , 323 )




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