Red rot. (Courtesy of Geof Huth)n.the process of leather deterioration characterized by orange or reddish powder 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.
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.