| Prevention and treatment of mold in library collections with an emphasis on tropical climates: A RAMP study |
|3. Implications for library materials|
|3.1 Vulnerability of materials|
Tanned leather is more resistant to mold growth than untanned leather. Chrome tanned leathers are relatively impervious, vegetable tanned leathers considerably less so. Book leathers are, unfortunately, vegetable tanned, chrome leathers being used primarily in shoes, luggage and other such items.
Studies indicate that mold growth does not affect leather in the same way that it does cellulose. The mold apparently does not attack the hide-tannin complex itself.
Barghoorn has demonstrated that invasion and destruction of the collagen aggregates of the hide substance does not occur; and Hyde, Musgrave and Mitton have shown that vegetable-tanned leathers suffer surprisingly little damage through even fairly heavy and prolonged mold growth. Experimental evidence indicates that the major cause of tropical deterioration of leather is hydrolytic breakdown due to the high atmospheric humidity and temperature and to their effect on interfiber lubrication, the extent of the hydrolysis being dependent upon the pH of the leather.5
Thus, it seems that the components of leather which support mold growth are the lubricants, the conditioning materials and the finish. It would seem from the literature cited above that high ambient relative humidity rather than mold damage is the primary cause of deterioration of leather in tropical climates.
Oiling of leathers, which many libraries have viewed primarily as a cosmetic treatment, may in fact be the most viable way of protecting leather in a tropical environment. Some libraries in tropical climates have avoided leather dressings, fearing that the use of oils and lubricants would promote mold growth. However, since any resultant mold growth is superficial and causes no structural damage to the leather, and since the application of a leather dressing prevents the hydrolytic damage that is the chief cause of deterioration, the use of leather dressings of appropriate composition should be considered beneficial.
With regard to the choice of a particular leather dressing, experience in the tropics indicates that a very light coat of neatsfoot oil and lanolin, allowed to dry for 24 hours and then buffed with a soft cloth works well. Leather dressings containing wax, including one developed by the British Museum, do not harden satisfactorily in warm humid climates, and the surfaces of treated items tended to stick together when returned to the stacks.