Cleaning Plastics
A Guide by Sophie Budden, Conservator

The subject of cleaning plastics is controversial. This guide by Sophie Budden, a specialist in decorative arts conservation, is the first to be published by plastiquarian and is intended to initiate dialogue. It is geared towards the delicate cleaning of objects from a conservators point of view, namely: any treatment carried out should be reversible; the object should suffer minimum interference and should never be damaged; and cleaning procedures should not cause adverse damage in the long term. Certain abrasives, such as T-Cut, have been included in the text, but should only be used as a last resort, or if the restoration of colour is essential.

Later this year the first authoritative guide, Conservation of Plastics by John Morgan, will be published by the Museums & Galleries Commission as part of the joint PHS/Conservation Unit initiative on caring for plastics.

Objects are cleaned not only to improve their appearance but to increase their stability. In many cases it may be necessary to clean and object prior to any other treatment, such as repair.

The correct identification of a plastic is essential before any cleaning is undertaken, as the cleaning process is determined by the specific composition of that individual piece. Identification is difficult but can be done, and experience and knowledge help. All cleaning agents should be tested first on a small, unobtrusive area to avoid damage, and agents containing ammonia must never be used.

Certain plastics contain plasticisers which have a tendency to migrate to the surface over a period of time and can collect dirt. They can be removed by careful cleaning, but not with solvents. Any cleaning method which is likely to remove the surface should be avoided. Dirt and dust particles may also adhere to plastics by electrostatic attraction. Excessive polishing can increase this attraction and should be avoided. The use of a non-ionic detergent such as Synperonic N or a mild household detergent, both of which should be diluted in distilled water and applied with cottonwool swabs, will remove surface dirt. Cleaning agents should always be rinsed off.

Some commercially available polishes will clean plastics without damaging existing patinas. Two produced by Greygate Chemical Products are specifically made for plastics: one is for cellulose acetate, the other for general use. These polishes were originally developed for polishing helicopter windscreens and contain a 13 micron abrasive. Other useful products are Solvol Autosol Chrome Cleaner and Black Cleaner, T-Cut and Duraglit. The chrome cleaner is slightly coarser than the black cleaner which is a white paste used for fine finishing. Home-made pastes of alumina, tin oxide or jewellers’ rouge mixed with distilled water should produce a basic but reasonable cleaning agent.

SOME SUGGESTIONS FOR CLEANING SOME SPECIFIC PLASTICS

All the plastics listed below can be gently cleaned with a dilute solution of non-ionic detergent, such as Synperonic N, preferably in soft water. Rinse thoroughly and dry carefully. Occasionally, apparently solid plastics mouldings include a foamed layer. it is important that water is not allowed to get into contact with these materials.

Acrylics are prone to crazing if organic solvents are used. Fine abrasive polishes are produced for acrylic by ICI and Rohm & Haas.
Use water sparingly on Casein. A wax polish can be beneficial.
Cellulose acetates contain plasticisers. Use Greygate Polish formulated for cellulose acetate, or acrylic polishes.
Cellulose nitrate (CN) also contains plasticisers. It is soluble in organic solvents and excess moisture can be detrimental.
Polycarbonates are susceptible to yellowing and can become brittle. Chemicals such as ammonia and other alkalis are detrimental.
PVC often contains plasticisers. Those which migrate to the surface and collect dirt can usually be removed using a non-ionic detergent.
Polyethylene/polypropylene embrittle with age and are liable to crack.
Polyurethane usually resists solvents but can swell, and become brittle with age.
Phenol formaldehyde resins (Bakelite): after cleaning polish with Solvol Black Cleaner or a household wax polish.
Urea formaldehyde can be polished with a wax polish after cleaning.
Melamine can be cleaned with non-ionic detergent and/or Solvol Autosol or Black Cleaner, which are white pastes which will not damage the surface shine.
Nylon will darken on exposure to light and can absorb moisture, so use water sparingly.