Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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A colloidal, lusterless, fine-grained, earthy substance which generally develops plasticity when wetted but is permanently hard when fired. Chemically clays are aluminosilicates, which do not form large crystals. The finely divided aluminosilicates, which are responsible for the properties associated with clays, are called "clay minerals." Clays with a preponderance of the clay mineral "kaolinite" are used both as fillers and as coating pigments in the manufacture of paper. Other clays are used in small amounts. Used in excess, as it is in some art papers, clay becomes an adulterant to the detriment of the strength and durability of paper. See also: ATTAPULGITE CLAY ;BENTONITE ; KAOLlN; PAPER CLAY .

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