n.a white, crystalline substance usually formed from salts that precipitate out of leather, often in humid conditionsGottlieb 1982, 37A crystalline efflorescence, which appears primarily on pre-19th-c. Leather [sic] bindings in the University of Chicago Library, Department of Special Collections, was analyzed by Nuclear Magnetic Resonance to be lactic acid salts.UIUC 2014Efflorescence can affect a number of materials, including stone, concrete, and leather. It occurs when the amount of moisture in an object exceeds the amount of moisture in the air around that object. This causes the moisture to migrate towards the object’s surface. Once the moisture reaches the surface, it evaporates, leaving behind any salts that may have been dissolved in it. ¶ Leather bindings often contain salts left over from the tanning process. . . . ¶ When books are sitting next to each other on a shelf, the efflorescence tends to appear only on their spines and top edges, as these are the only places where the leather is exposed to the air. The powder has no harmful effects, and a single swipe of the finger will remove it.Burns and Schoenborn 2017The difficulty with this disaster was that white mold is very difficult to distinguish from efflorescence which is also white. Visually efflorescence looks like white dust spread over an area of the book. On the spines of books it is concentrated in areas of depressions, ridges, or lettering. Efflorescence is not a fungi but a crystalline residue caused by deteriorating leather dressing previously applied to help preserve the binding. It was intended to help the leather cover stay supple.Bawden 2021You might also come across efflorescence, white crystals which occur from salt dissolved by humidity.NEDCC 2021, 2Other types of damage commonly mistaken for mold include dirt, foxing, and efflorescence. Foxing is characterized by reddish-brown spots that appear on paper. Efflorescence appears when fats and salts in leather or heavily starched cloth crystalize and form a precipitate. Efflorescence has a white, crystalline appearance. Both problems can be caused by high levels of humidity. While unsightly, these problems are harmless and are not a cause for concern.
