"Bloom" on leather and many other objects can arise from at least two different sources and has correspondingly different chemical composition and should be treated differently. One source is mold, a biological source, probably arising from a sufficiently long exposure to relatively humidity high enough to promote mold growth. A second source is migration of fatty materials, typically fatty acids like palmitic and stearic acid, from the bulk of the leather to its surface where crystallization of the acids occurs. These two types of bloom can be readily distinguished by low power stereomicroscopical examination. Molds shows fluffy and filamentary structures that are now smeared by wiping with a needle, whereas fatty acids are waxy, non-filamentary, perhaps fuzzy crystals, easily smeared by wiping with a needle. Different methods for removal of the two types of bloom are required. Fatty acids are insoluble in water but are soluble in mineral spirits and other non-polar or very slightly polar hydrocarbon solvents and may be removed with very slightly moistened swabs. Unfortunately, since the source of the fatty acid bloom is fatty materials in the leather (either natural in particularly high fat content leathers, or added by such products are saddle soap and leather dressings) these fatty acid blooms are likely to redevelop over time. Fatty acids blooms apparently develop because there is an incompatibility between the fatty acids and the materials in the leather in which the fatty acids were dissolved initially. This incompatibility may have always been present and just becomes noticeable after sufficiently time passes for the fatty acids to migrate from the body to the surface. Or, incompatibility may develop as the chemical composition of the object changes with time, primarily by oxidation, hydrolysis, and crosslinking of the compounds in the object. Oxidation may increase the polarity of the object, crosslinking may reduce the molecular free volume of the fatty phases, and hydrolysis of soaps and fatty oils may produce higher concentrations of free fatty acids that can migrate. These reactions are all affect in a very complicated way by environmental conditions, particularly relative humidity. Decreased air circulation may contribute to fatty acid bloom production. It has been observed that bloom forms more often on oil paintings and prints that are framed behind glass, than on paintings that are not glazed (Williams, R.Scott, "Blooms, blushes, transferred images and mouldy surfaces: What are these distracting accretions on art works" Proceedings of the 14th Annual IIC-CG Conference, May 27-30, 1988, Toronto, Canada, pp. 65-84). The advisability of trying to remove fatty acid blooms should be considered. Aside from the unsightly appearance of the fatty bloom, there is probably not much fear that the leather object will be further damaged just because this fatty acid bloom is on the surface. The entire object is probably saturated with the fatty acids or compounds that break down to produce the fatty acids (such as neatsfoot oil and soaps so commonly found in leather dressings) so that removing the fatty acids from the surface will have little effect on the overall fatty acid content of the object. Since there could be damage to other objects that come into contact with this bloom, direct contact between this and other objects should be avoided. Also there may be reaction of the fatty acid bloom with other components of the object such as metal fittings or fastenings, that may be corroded by the fatty acids, especially copper based alloys. Such a situation would definitely warrant removing as much fatty acid bloom as possible, and the physical isolation of the fitting from the fatty leather surface (perhaps for example by polyester or polyethylene plastic sheet separators between fitting and leather). Mold is not soluble in water or mineral spirits. If the mold is embedded in a layer of fatty material, then dissolution of the fatty material may also remove the mold, but this is a secondary effect. In general mold must be removed by some sort of physical or mechanical process perhaps aided by cleaning solutions. Also, since mold is biological in origin and will grow if conditions are right, some process to kill the mold might be considered. Such treatments are beyond my experience and information for this must be obtained from someone else. ______________________________ Reply Separator _________________________________ Subject: Treatment of leather Author: Museum discussion list <[log in to unmask]> at INTERNET Date: 3/15/96 9:52 PM We have in our collection leather bridles, halters, reins, saddles, saddlebags and so forth that have a white "bloom," which I'm assuming is mold. It wipes clean, and I've used basic saddle soap which also removes the film. The items are stored in a climate controlled HVAC building, but I'm wondering if there isn't enough air circulation. Has anyone else had this problem? Please, no lectures about calling conservators. This is just a topic for conservation and feedback. Thanks. The following is an attached File item from cc:Mail. It contains information that had to be encoded to ensure successful transmission through various mail systems. 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