Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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rosin size

A solution or dispersion obtained by treating ROSIN with a suitable alkali. The resulting size may be fully saponified or it may contain free rosin acids. When properly converted in the papermaking process, usually by the addition of ALUM , the size precipitates and imparts water (ink) resistance to paper. Since in its natural state rosin is insoluble in water; it must be altered chemically before it can be used as a sizing material. Although several methods of treatment exist, the one in general use today is basically the same as that used in the manufacture of soap, i.e., saponification of a portion or all of the rosin with caustic soda or soda ash to form a soluble rosin soap. Unreacted rosin, which is held as an emulsion, is known as free rosin. The percentage of free rosin has been found to affect the sizing efficiency of a material to a certain degree, the extent depending on variations in conditions in local paper mills. (17 , 98 , 143 )

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