cellulose-based products such as paper or, in particular, the starch-based adhe-
sives used to attach leather bindings to book boards. The various wood-boring
beetlesare also quite capable of passing through leather on their way in and
out of a wooden structure underneath.
From time to time, conservators are asked to repair physical damage caused
by vertebrate pests. In the author’s experience these include mice, squirrels,
cats, dogs, small boys and a parrot. No doubt other conservators can add to
this list.
4.3 Chemical Deterioration
Leather can be considered as a relatively chemically-stable material. In general
objects made from leather reach the end of their useful lives as a result of fair
wear and tear rather than chemically-induced decay. If a pair of shoes lasts for
10 years or a wallet or briefcase for 20 years, the owner is usually satisfied.
Books are different. Many leather-bound books spend the majority of their
lives sitting unused on shelves. Libraries in historic houses, for instance, contain
thousands of books which are rarely read but whose bindings remain sound
after a century or more. It is not surprising, therefore, that when in the middle
of the nineteenth century it was discovered that many new bindings were
deteriorating rapidly, an explanation was sought.
The first systematic investigation into the problem was undertaken for the
Athenaeum Club in 1841 by a committee of tanners and chemists chaired by
Michael Faraday. The cause of the rapid decay was shown to be sulfur diox-
ide given off by the newly installed coal gas reading lamps, which oxidised
and hydrated to form sulfuric acid within the leather fibrous structure. As the
century progressed leather bookbindings from libraries without any gas light-
ing were also found to suffer from the same form of deterioration, which
became known as red rot. Further work was carried out under the auspices of
the Royal Society of Arts. Their report confirmed that the major cause of red rot
was the presence of sulfuric acid in the leather. This could either have come
from sulfur dioxide pollution in the atmosphere or have been added during the
tanning processes. They also concluded that leathers tanned with hydrolysable
tannins were superior in their ageing properties to those processed with con-
densed tannins.
In the 1930s, a major study was undertaken to determine the effects of
different environmental conditions on over a hundred commercially- and
experimentally-prepared leathers. Duplicate sets of books were bound with
these. One set was shelved in the British Library, representative of conditions
in a polluted urban atmosphere and the others in the National Library of
Wales in Aberystwyth, a clean rural setting. The books were examined at reg-
ular intervals over a period of nearly 50 years for evidence of degradation.
112 Chapter 5