Treatment for Acid Deteriorated Leather (Red Rot)

The Leather Conservation Centre has developed a new treatment for acid deteriorated leather (commonly known as red-rot).

This new conservation treatment for acid deteriorated leather is a service that can only be provided by The Leather Conservation Centre.

The product, which has been stringently tested, works by reducing the acidity of the leather (as evidenced by raised pH levels) and stabilising the collagen fibres (as evidenced by a rise in the shrinkage temperature).

The two year research project, which was led by a full time leather chemist (Dr Anne Lama), was carried out in conjunction with the University of Northampton (School of Leather Technology) and was funded in part by the Centre and part by the UK Technology Strategy Board.

The Centre’s conservators and other leading conservation professionals from other major UK institutions had significant input into the development of this product with particular regard to conservation and ethical requirements.

To ensure its acceptability within the conservation profession, a seminar and workshop was held at The British Library in the summer of 2011, attended by senior conservators from national museums, libraries, archives and other institutions. One senior conservator from a major national museum commented “this is the best thing to happen in leather conservation for 30 years.”

Acid-deterioration occurs in vegetable-tanned leathers that were predominantly manufactured from the mid-19th century onward, and has been observed in a variety of leathers (including bookbindings, gilt leather, screens, wall hangings, upholstery and luggage). The deteriorated leather shows a lower pH, sometimes below 3.0, and lower hydrothermal stability generally expressed as shrinkage temperature (which may be as low as 30C), indicating the loss of collagen structures. The visible changes in the deteriorated leather usually include fine cracking, a powdery surface (often reddish/brownish and hence the common term for acid-deterioration is red-rot) and complete or partial loss of the grain layer.

The product has been applied to 100s of test samples of historic leather and new artificially aged leather and these samples have then been artificially aged in the Centre’s ageing chamber (using set rates of exposure to sulfur dioxide (SO2) and nitrogen dioxide (NO2), temperature and humidity). The leather samples were tested for acidity levels and shrinkage temperature before and after ageing (at the equivalent of 25, 50, 75 and 100 years ageing) and the data compared with untreated, un-aged, control samples. The results show that after treatment there is a rise in pH (indicating lower acidity) and a rise in shrinkage temperature (indicating a stabilisation of the collagen fibres) in almost all cases. In a few cases where the leather was heavily deteriorated no shrinkage temperature could be obtained (before or after treatment) indicating that the leather had broken down completely.

The Centre’s conservators have been trained in the specialist procedures required for the application of this new product and it is now included in the comprehensive range of conservation treatments available at the Centre.

If you have any books or other objects within your collection which have acid deterioration, the Centre would be happy to carry out treatment either at the Centre’s fully equipped studios, or on-site.

If you are unsure as to whether acid deterioration is present in any leather, then a visit by one of the Centre’s conservators can be arranged to determine the extent of any damage.

Please email Yvette Fletcher, Head of Conservation at The Leather Conservation Centre – lcc@northampton.ac.uk – for further information and an estimate of costs.