Series editors' preface - Wood Tools

354 Conservation of Furniture
Paper pH testing strips make use of this
property. The iron mordants used in the printing
and dyeing of dark colours accelerate
degradation of the fibre (Storey, 1978). Iron
acts as a catalyst for the conversion of sulphur
dioxide to sulphuric acid. The acidic conditions
combined with the energy from light
cause degradation. Dyes may bleed either in
wet cleaning or in high humidities. Sulphur
dyes contribute to sulphur reactions.
Another type of reaction that may occur is
the photochemical degradation of textile fibres
catalysed by the presence of certain dyes of
high light fastness, a phenomenon known as
tendering. Various direct, acid, basic, sulphur,
vat and disperse dyes of many different
colours sensitize the photochemical degradation
of cotton, viscose, rayon, silk, nylon and
acetate fibres, providing oxygen is present.
When cotton dyed with a tendering dye is
exposed to light under moist conditions hydrogen
peroxide is formed. The complex mechanisms
by which this may occur are discussed
by McLaren (1983). Some of the energy of the
excited molecules may be transferred to
oxygen molecules promoting them to an
excited state in which they may react with
water present in moist air to form hydrogen
peroxide. Alternatively, the dye in an excited
state may react with the substrate by a process
of hydrogen abstraction to create a ‘free
radical centre’ which is then attacked by
molecular oxygen. In both mechanisms, the
dye behaves as a catalyst for photo-tendering
by oxygen in the air. The relative importance
of the two mechanisms remains unclear but in
any case it is not necessary to propose an
exclusive mechanism. For further information
on this subject see Tímár-Balázsy and Eastop
(1998).
Finishes also affect the textile and its degradation.
Starches are foodstuffs for moulds
which may stain textiles during their digestive
process. Formaldehyde is used in finishing
some textiles and in some leather tanning
processes. It is often used in the manufacture
of ‘permanent press’ fabrics, as the primary
crosslinking agent. Exposure of proteinaceous
materials to formaldehyde may result in loss
of elasticity (Carpenter and Hatchfield, 1986).
Animal glue, for example, is crosslinked by
formaldehyde. Formaldehyde is a reducing
agent that can discolour metal oxide pigments
and make cotton, wool and leather brittle by
linking two alcohol or amino groups in the
polymers making up those materials (Berndt,
1987). Formaldehyde can also be transformed
in the presence of oxygen to formic acid
which can react with a variety of materials in
a similar manner to acetic acid. For further
information on this subject refer to Tímár-
Balázsy and Eastop (1998).
Preventive conservation of textiles
The recommended environment for textiles is
a constant relative humidity within the range
50–60%. In conditions of low relative humidity
these materials are prone to embrittlement
whilst in high RH levels they are subject to
bio-predation. A temperature of 18 °C is
recommended as a reasonable compromise
between the needs of objects, people and
effective RH control. Exposure to light should
be as low as possible. Light should be filtered
to remove UV radiation and should be kept to
the minimum needed for the purpose, preferably
not exceeding 50–100 lux for continuous
exposure. Air should be filtered to remove
particulate pollutants and gases such as oxides
of sulphur and nitrogen if possible. Removal
of particulate pollution is probably the greatest
single cause of damage and it is therefore
most important to reduce the frequency with
which this needs to be done, particularly for
textiles with degraded fibres. In storage,
materials in contact with textiles or in close
vicinity to them should be acid-free.
Unbuffered materials are recommended.
However, buffered materials can be used next
to most cellulosic materials. When handling
textiles, gloves should be worn to protect
them from acidic and oily skin deposits.
Alternatively, where gloves themselves might
pose a risk, hands should be washed and
thoroughly dried as required during handling.
For further information see Landi (1992/1985),
Flury-Lemberg (1988) and Tímár-Balázsy and
Eastop (1998).
Plastics
Plastics and rubbers, whether synthetic or
natural, deteriorate continuously from the time
of manufacture. Deterioration of plastics and
polymers is discussed in general terms in
section 8.8. At the molecular level, polymer
chain sizes, structural organization and other