Plastics and rubbers form a significant part of our cultural heritage. They are found not only in art, historic and technological collections, they are also among the ethnographic materials of the twentieth century. Objects made from these materials range in diversity from radios, clocks, fountain pens, jewellery and hair accessories, to plastic robots and dolls, and all are becoming increasingly collectible.
Plastic is a generic term covering all types of synthetic materials. These different types of materials may differ dramatically from each other with respect to their care requirements. It is, therefore, most important to try to identify the type of plastic from which the object is manufactured.
Plastics are commonly classified on the basis of their origin:
Although the unambiguous identification of a plastic material requires the use of sophisticated equipment, sometimes an 'educated guess' is sufficient. The probable date of the object, the appearance, feel and smell of the material, and the properties necessary for its use are important clues. For example:
A conservator specialising in this field can help you identify the material and manufacturing process used in making your object or collection. This will help you catalogue and document your items and give you clues as to how best to keep them in good condition.
Cellulose nitrate is affected by light and moisture and releases potentially dangerous chemicals during degradation. Do not store items made from this material in plastic bags or other packaging with restricted ventilation. Early signs of breakdown include a smell of camphor, disintegration of wrapping tissue, surface bloom and yellowing.
Note that cellulose nitrate-based film may deteriorate and disintegrate at room temperature. Cinema film in particular can combust spontaneously. All cellulose nitrate film stock should therefore be isolated, and advice on storage sought from the Fire Brigade.
Cellulose acetate degrades in a similar manner to cellulose nitrate, but with the production of acetic acid, hence the vinegary smell. The migration of plasticiser to the surface of the object can results in a “tacky” surface.
The main breakdown problem associated with PVC is the loss of its plasticisers. This results in a sticky deposit on the surface which attracts dirt, and in the material becoming more rigid and liable to crack and go yellow.
The problems most usually associated with this material are cracking and splitting due physical and environmental stresses.
Storing plastics at low temperatures and relative humidities will slow down the rate of degradation reactions. Plastic objects should also be kept in low light levels.
Some objects require special care, especially those made from cellulose nitrate and acetate. These should be stored in a cool, dry atmosphere. Never store them in humid surroundings such as laundry rooms as this can cause warping.
If objects show signs of degradation - such as a smell of vinegar or camphor, it is best to separate them from other objects. Either leave the plastics loosely covered with acid-free tissue or even silicone paper to stop dirt getting at them if there is a strong acid smell. If there is any surface acid you could remove it with a dry tissue (it might stick, so be careful), or a very lightly water-moistened one, but do dry the surface carefully afterwards.
As solvents may react with specific plastics, causing stress-cracking it is best to avoid their usage. Mechanical “dry” cleaning such as brushing and dusting is the best way to remove surface dirt. You can also use cotton swabs dampened slightly with water, but make sure the surface is dried thoroughly afterwards.
As owner and collector of plastic items, you can prevent damage by improving storage and protection as above, but there are instances where a conservator experienced in this field can provide invaluable help.
Use the Conservation Register to Find a conservator.
© Icon, the Institute of Conservation 2011.
This article offers general guidance and is not intended to be a substitute for the professional advice of an accredited conservator. The views expressed are those of the author or authors, and do not necessarily represent the views of the Institute of Conservation.
The Institute of Conservation would like to acknowledge use of the MGC publication 'Ours for Keeps' in the preparation of this text. The Institute of Conservation and its partners accept no liability for any loss or damage which may arise if this guidance is followed.
The Institute of Conservation would like to acknowledge the support of The Royal Commission for the Exhibition of 1851 in the production of this guidance information. Further information on The Royal Commission for the Exhibition of 1851 and its work is available at www.royalcommission1851.org.uk.