What is red rot?
Red rot is a type of deterioration of the surface of tanned leather occurring when certain (usually vegetable) tannins degrade to a fine red powder. The causes of this decay is complex, and not entirely understood, although tanning products introduced in the 19th century and atmospheric pollutants are known to be two contributing factors. Unfortunately this type of decay is an all-too-familiar sight in collections of leather bound books and other leather objects, it is particularly prevalent in, although not restricted to, books produced in the latter half of the 19th century.
How to distinguish red rot
Red rot is characterised by a reddish, powdery surface that crumbles to the touch, made worse by handling. At an advanced stage the entire binding can resemble reddish suede and may peel away in strips from the covering boards. Red rot also produces a characteristic, somewhat acrid smell. The powdery ´dust´ emanating from this type of deterioration is made up of tiny particles of acidic, decayed leather, and may cause mild to moderate skin irritation, especially for those in prolonged contact with it. Minor localised rashes, itching eyes or an allergic reaction similar to hay fever, such as sneezing, coughing or runny nose are not uncommon.
Treatments and remedies
Once underway, the disintegration of leather caused by red rot cannot currently be reversed. Its progress can, however, be slowed down by means of improved environmental conditions and storage, and a reduction in the level of natural light.
The best way to achieve this is to wrap the book in acid-free tissue and store it in a box made from good-quality board. This is a simple, cost-effective way of immediately reducing the rate of deterioration, limiting the potential for further physical weakening of the book´s structure and also minimising the risk of irritation to the owner caused by handling or close proximity to affected bindings.
A number of different approaches to treat red rotted leather have been attempted, such as buffering or neutralizing the leather. At this stage though the long-term efficacy of these treatments is still uncertain. Another potential way of consolidating the powdery red rot is to apply a consolidant to the surface. However, this is only a surface treatment and will not improve or correct the underlying causes of decay. One of the major disadvantages of using consolidants is that sometimes they have been known to cause a darkening or staining the leather surface. It is not generally a helpful solution for large surface areas. The decision to use a consolidant should only be taken by an experienced and qualified conservator and professional advice should always be sought in advance.
