116 Chapter 5
The conservation treatments applied to a leather object may include recording,
pest eradication, cleaning, reshaping, repairing, reinforcing, infilling, inpaint-
ing, consolidation, chemical stabilisation and surface coating. The choice of
techniques and materials employed for each of these stages is often based on
previous, scientifically-based investigative work. This includes studies such as
those into the strength and flexibility of repair materials, the stability of adhesives
and the penetration of consolidants into fragile substrates. This section will,
however, concentrate on treatments developed for the major causes of deteri-
oration of leather objects.
5.1 Biological Deterioration
As is the case with most conservation strategies, preventing biological attack
is far preferable to treating the results. It is known that at temperatures normally
experienced in temperate climates, such as Northern Europe, mould will not
grow on leather at relative humidities of less than 65%. Leather objects
should therefore be kept away from damp walls, and efforts should be made
to circulate the air in display and storage spaces to prevent the build up of
moist, damp areas. In many countries, relative humidities in excess of 65%
are commonly experienced and the cost of dehumidification prohibitive. In
these cases, the only option is the use of a suitable fungicide. A large number
of these have now been withdrawn because of health and safety regulations. The
products currently most widely employed in the leather-producing industry
to prevent mould growth are based on 2(thio cyano methyl thio) benzothiazole,
TCMTB. Despite the somewhat chemophobic attitude of many curators and
conservators, this material has been used successfully where climate control
is impossible.
Just as the routine use of chemical fungicides is being avoided, insecticides
are now only being employed where absolutely necessary. The preferred tech-
niques are the use of cold, heat or anoxic atmospheres. Freezing the object
to25°C for a period of 24 h has been shown to kill virtually all insects. Care
must be taken to wrap the object properly to prevent the formation of poten-
tially damaging condensation as it warms back to ambient temperatures.
Heating an object approximately 50–55°C will also kill all insect pests.
Provided the humidity of the object and its surroundings is carefully controlled
as with the Thermo Lignum process, a wide variety of skin materials can be
satisfactorily treated in this way.
5.2 Chemical Deterioration
As has been stated, the most widespread form of chemical deterioration
found in historic leather collections is the result of a combination of oxidative