Series editors' preface - Wood Tools

272 Conservation of Furniture
in keratin found in hair, horn and turtleshell
and sulphur bonds in rubber and some
leathers. While some commercial fumigators
today are still using materials such as methyl
bromide, hydrogen cyanide and sulphuryl
fluoride on common household furniture and
on museum objects there is a growing
movement towards the use of safer alternatives
based on control of temperature and oxygen
levels. Furniture conservators will need to be
well informed about the side effects of each
fumigant on a wide range of materials, since
furniture often incorporates other materials such
as upholstery fabric, leather, proteinous glues,
varnishes, paints, metals, plastics, etc.
Treatments based on raising or lowering
temperature must take into account the effect
on RH and the possibility of dimensional
change in wood and other materials, such as
metals, incorporated into the object.
Temperature treatments may be problematic
for wooden components of large dimension
since wood is an effective insulator and may
protect larvae in the core. Temperatures of
–25 °C to –30 °C maintained for two to three
days will kill all stages of the insect infestation.
Living tissue contains 90% or more water.
The effects of freezing include dehydration,
osmotic swelling, loss of bound water and ice
formation within the insect’s system, all of
which are lethal. Objects with stratified layers,
such as decorative surfaces, inlaid or veneered
surfaces may not be suitable for freezing.
Objects are often placed into plastic bags
which may be aspirated using a vacuum or
buffered to prevent potential damage from
condensation in the bag as the temperature
falls. Freezing treatments are widely used for
textiles (Blyth, 1997). Raising the temperature
above 50 °C is reported to kill all stages of the
insect life cycle in less than an hour
(Nicholson, 1997). The relative humidity must
be kept constant to avoid the risk of damage
to organic materials. The effect on adhesives
and surface coatings of raising the temperature
has not yet been fully investigated.
Low oxygen environments offer an alternative
to insecticides. Gilberg (1989, 1990, 1991),
Hanlon et al. (1992), Koestler (1992) and Rust
et al. (1992) have experimented with replacing
the air in a closed container with the inert
gases nitrogen or argon. It has been demonstrated
that stages of the insect life cycle are
killed by lack of oxygen after a fourteen to
twenty-one day cycle, depending on the type
of gas, the tolerance of the insect species,
temperature, relative humidity and oxygen
concentration. Objects are usually placed in a
gas-tight bag and the air replaced by flushing
it with an inert gas such as nitrogen, argon or
carbon dioxide. It is essential that the relative
humidity is maintained at an appropriate level
for the object being treated. The oxygen level
can vary depending on the gas used and is
measured with an oxygen meter. Oxygen
scavengers may be placed in the bag to further
reduce the oxygen level, but should not be
placed in contact with the object as they
produce heat. The system may be active, in
which the flow of gas is maintained throughout
the fumigation cycle to compensate for
leakage, or passive, in which gas flow is
stopped and the bag sealed with an oxygen
absorber inside. When the cycle is completed
the bag is vented and the object removed.
The advantages and disadvantages of a wide
range of the methods available, including
heating, freezing, low oxygen atmospheres,
radiation and chemical agents, are further
discussed by Pinniger (1994, 2001) and by
Umney (1997). The use of inert gases in the
control of museum insect pests is the subject
of an extensive recent publication by Selwitz
and Maekawa (1998).
When all the stages of dealing with an insect
infestation have been completed, it is usually
necessary to institute a monitoring programme,
usually incorporating the use of blunder traps,
to ensure that the treatment procedure has
been successful and to identify any fresh
outbreaks before substantial damage can be
caused to objects. Fresh woodworm exit holes
are usually light coloured and may need to be
toned to a darker colour in order to be able
to monitor for possible re-infestation.
An essential corollary to treating individual
objects is addressing the environmental conditions
which may have fostered the initial
outbreak. This may include surveying the
building in which the outbreak occurred and
identifying vulnerable materials or objects,
areas with high temperature or relative humidity
and dead spaces, both in display and
storage areas and those, such as chimneys or
attics, incorporated into the architecture of the
building. A high standard of housekeeping will