Red rot

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Contributions by: Eva Falls, Lucas Simonds

The term red rot refers to a process of leather deterioration observed commonly in vegetable-tanned leathers from the late nineteenth and early twentieth centuries and infrequently in leathers from earlier periods (Kite and Thomson 2006:253). Although red rot appears most commonly as a red dust on the surface of the leather the associated deterioration processes affect the fibrous structure of the leather, and if left untreated, leather suffering from red rot can disintegrate completely into a red powder (Waterer 1972:126). A powdery red substance forms on the surface of the leather when exposure to acids leads to “polymerization of the tannin to form brick-red phlobaphenes.” Cronyn 1990

An example of leather exhibiting red rot from the shaft of a horse-drawn vehicle, c. 1880

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While red rot is not completely understood, it is generally considered to be a caused, at least partially, by the action of strong acids, in particular sulfuric acid. Such acids may have been added to the leather intentionally during the tanning process, but could also form as a result of the absorption of sulphur dioxide, a compound often found in pollution (Kite and Thomson 2006:62). The sulfuric acid attacks and breaks down the protein chains that comprise the leather object. Soest et al. 1984 Leather breakdown by acids can also be attributed to past tanning or original assembling exposure. It is often seen in leather bound historic books, because of binding agents or certain paints Soest et al. 1984, and in vegetable tanned leathers Cronyn 1990. Although it has been shown that leathers with a pH below 3.2 are far more likely to develop red rot, in a study from 1975 a sample whose pH was measured as 2.6 in 1931 showed no signs of deterioration whereas a sample whose pH was measured as 6.5 showed significant deterioration (Kite and Thomson 2006:62). Unfortunately, the effects of red rot are irreversible (Kite and Thomson 2006:232); therefore, treatment plans focus on the prevention of further damage rather than repair. The simplest treatments entail improved storage conditions, and an affected piece of leather stored in an archival quality box and wrapped with acid-free paper will show a significantly reduced rate of deterioration (National Archives 2012). Overall, leathers should be exposed to a neutral to only slightly acidic environment. Soest et al. 1984 Red rot is addressed by conservators during the consolidation stage of treatment Morris and Seifert 1978. More advanced treatments involve the use of sealants and consolidants to hold the deteriorated leather together and limit further deterioration. The most common of these treatments is known as the red-rot cocktail,î and is a mixture of S6000 (an acrylic/wax coating) and Klucel G (a consolidant). Although both S6000 and Klucel G produced some adverse effects when applied on their own, the mixture of the two limits those effects while also providing strength to the leather and limiting the absorption of further pollutants (Kite and Thomson 2006:232). A number of other treatments have also been used with some success (Waterer 1972), but the goal remains the same; to consolidate the deteriorated leather and seal it from further deterioration. The leather is structurally breaking down and without attention will eventually become dust Waterer 1972. In addition to concerns over the state of the leather, conservators must also take care around red rot, as the red ìdustî can pose a number of health risks including minor skin irritations and symptoms similar to hay fever (National Archives 2012).

See Also:“Leather and Skin”[1]

Picture Reference: Connecticut State Library Preservation. “Bound Volumes.” [2]

References

Cronyn, J.M. 1990. The Elements of Archaeological Conservation. Routledge. New York, NY: 271.

How to Deal with Red-Rotted Bindings. 2012. National Archives Collection Care FAQ. National Archives, UK. [3] (accessed 4/15/2013).

Kite, Marion and Roy Thomson eds. 2006. Conservation of Leather and Related Materials. Oxford, UK: Elsevier

Morris, Kenneth and Betty L. Seifert. 1978. Conservation of Leather and Textiles from the Defense. Journal of American Institute for Conservation 18(1):33-43.

Soest, H.A.B. van, T. Stambolov, and P.B. Hallebeek. 1984. Conservation of Leather. Studies in Conservation 29(1): 21-31.

Waterer, John W. 1972. A Novel Method for the Conservation of Fragile Leather. 1972. Studies in Conservation 17(3): 126-130.


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