Red rot. (Courtesy of Geof Huth)n.the process of leather deterioration characterized by orange or reddish powder Vogt-O’Connor and van der Reyden 1996, 1Wrap books in historic house libraries in polyester four-flap enclosures to provide protection from red rot.Ritzenthaler 2010, 77Leather is naturally acidic by virtue of the tanning process. However, excessive acidity in leather results in a condition known as “red rot,” which eventually can cause leather to become hard and brittle so that it deteriorates to a crumbly reddish-brown powder.Avery 2013This 19th century leather cover is weak, cracked and exhibits the phenomenon known as “red rot” that manifests in a powdery red layer of rotted leather under the cracking, paper-thin surface. This could be caused by use of sulfuric acid in the dyeing process.NEDCC 2022, 9For volumes with powdery leather bindings (“red rot”), use a box or construct a polyester film jacket and then place call numbers and labels on the enclosure, simultaneously labeling the volume and protecting adjacent volumes from the red rot.UIUC 2023Red rot is a type of deterioration particular to leather. It is common in leather bindings produced in the nineteenth century. The exact cause of red rot is unknown, but it is believed to be the result of acidic residue in the leather reacting to poor environmental conditions (pollutants and high heat especially). Red rotted leather is characterized as soft, powdery leather that crumbles into a reddish brown powder. There is no way to reverse this deterioration, but the leather can be consolidated so it does not crumble further. Consult a conservator before applying consolidants to objects. An alternative treatment, which does not stop the red rot but contains it for easier handling, is to cover the book in a polyethylene sleeve or wrap it in acid-free paper.
Red rot is most commonly found on vegetable-tanned leathers from the later 1800s and early 1900s. As a result of the tanning process, the leather is naturally acidic. Prolonged storage in or exposure to high relative humidity, environmental pollution, and high temperature affects the fibrous structure of the leather leading to the hardening and embrittling of leather and eventual disintegration into red powder if left untreated.