Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

 Previous item  Up One Level Next item

bloom

1. A deposit of ellagic acid formed in and on leathers tanned with vegetable tannins of the pyrogallol class, probably as a result of the action of enzymes native to the original source, i.e., bark, acorns, etc. Although bloom affects the physical properties of leather in that it increases weight yield, firmness, and water resistance, it is deposited in insoluble form and is not chemically combined with the fibers of the leather. Its presence at times gives an unsightly appearance to the leather. 2. A misty surface appearance in an illustration, caused by an excess of acid or too much drier in the ink. 3. The dulling film that sometimes appears on varnish and glossy paint films, particularly in industrial atmospheres. It usually consists of minute crystals of ammonium sulfate produced by the reaction between sulfur dioxide, ammonia, and oxygen in condensed moisture on the film. Bloom can appear on a freshly lacquered surface when rapid evaporation of the solvents causes the temperature of the surface to fall below the dew point. Moisture is deposited on the film, causing a limited precipitation of cellulose nitrate and giving the film a permanent cloudy appearance. (175 , 195 , 306 , 363 )




[Search all CoOL documents]


URL: http://cool.conservation-us.org/don/dt/dt0377.html
Timestamp: Saturday, 19-Nov-2011 13:18:39 PST
Retrieved: Tuesday, 21-Nov-2017 21:17:24 GMT