Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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potassium lactate

A potassium salt of lactic acid (KC 3 H 5 O 3 . H 2 O), used to treat leather in order to counteract acid present in the leather due to manufacturing processes or because of air pollution (sulfur dioxide), or as a safeguard against the future incursion of acid or acid-forming materials. It is used in an aqueous solution of 7% potassium lactate, 0.25% paranitrophenol (to inhibit mold growth), and distilled water. The potassium lactate is said to act as a buffering agent, e.g., 2KC 3 H 5 O 3 + H 2 SO 4 → K 2 SO 4 (potassium sulfate) +2C 3 H 6 ) 3 (lactic acid).

There is some controversy over the use of this salt as a leather/acid buffer. The major arguments against it seem to be that it may cause a whitish discoloration to appear on the surface of the leather (potassium sulfate discoloration) and, unless applied to the flesh and grain sides of the leather, it is ineffectual. If the latter argument is correct, it would mean that leathers used for bookbinding could be treated only one time.

Potassium lactate should not be applied to powdery (red rot) leathers, nor to suede leathers, as it will result in the blackening of both. (173 , 265 , 366 )

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