206 Chapter 8
Preventive conservation involves controlling the environments in which
objects are placed during storage and display, with the aim of slowing deteri-
oration reactions. Preventive conservation of plastics can either involve the
removal or reduction of factors causing degradation, such as light, oxygen,
acids and relative humidity, or of the breakdown products that accelerate
degradation. If applied successfully, such an approach can help to prolong the
useful lifetime of many objects simultaneously, so it can be considered an effect-
ive use of resources. Preventive conservation techniques are more likely than
active treatments to comply with the ethical practices of professional conser-
vators, primarily that of reversibility, as summarised in the code of practice:
‘The conservation professional must strive to select methods
and materials that, to the best of current knowledge, do not
adversely affect cultural property or its future examination, scien-
tific investigation, treatmentor function’. American Institute for
Conservation, 1994.Since there are no standard guidelines defining appropriate storage envir-
onments of museum objects containing plastics as a generic group, and cer-
tainly none specifying appropriate treatments for specific types of plastics,
those designed to preserve fragile organic materials such as feathers and plant
fibres are commonly applied. These include maintaining a stable relative
humidity, usually 553%, a temperature of 182°C, light levels between
50 and 300 lux and good ventilation if the object emits acidic gaseous degrad-
ation products. Although successful in reducing the rate of chemical degrad-
ation reactions, the use of low temperatures, particularly below 5°C is expensive
and inconvenient. The risk of thermal shock to the object and condensation of
moisture from air, as a result of its move from cold to ambient temperatures
when removed from a fridge (4–6°C) or freezer (20°C), is also a concern.
Dust should be prevented from contaminating the surfaces of objects by
covering with acid-free tissue paper or unbleached cotton; however, tacky
surfaces should not be covered with absorbent materials.
Specific preventive approaches to conservation have been used successfully
to prolong the useful lifetimes of collections containing cellulose nitrate, cel-
lulose acetate, PVC and polyurethanes. The microclimate surrounding plas-
tic objects can be readily and cheaply controlled by introducing an adsorbent
or scavenger into their storage areas.
5.1 Conservation of Cellulose Nitrate
Activated charcoal has been used successfully to dramatically reduce the rate
of degradation of cellulose nitrate objects. The charcoal is treated with oxygen