Care of Casein

With experience, casein plastics will become easy to identify. They have a distinctive smell when heated in warm water, or rubbed with an abrasive sandpaper - this can be learnt with practice using a known sample, such as a coloured plastic knitting needle (this will almost certainly be casein, but be aware that some needles marked in metric sizes may not be casein and occasionally one finds older needles in celluloid).

It should be remembered that moulded casein is very rare so objects which are obviously moulded to shape; i.e. have a mould parting line, are unlikely to be casein.

Casein plastics have a smooth, silky, natural feel which one can soon learn to appreciate.

Water is used during the manufacture of casein, some of it is retained in the material where it continues to act as a plasticiser, imparting a degree of flexibility. The main ageing problem is associated with changes in the amount and distribution of this moisture. Casein is hygroscopic and so it absorbs more moisture from the atmosphere when the humidity is high and loses it when heated or when humidity is low. Drying causes shrinkage and embrittlement, while reabsorption causes swelling and softening. The surface of the material is therefore subject to a changing stress pattern which can be likened to fatigue, albeit at a very low frequency. Eventually a network of fine cracks form over the surface of the material. This makes it more prone to moisture changes and with continued ageing, the cracks gradually expand and propagate into the material.

Other ageing problems are concerned with the effect of light, particularly strong sunlight. It causes yellowing and eventual blackening of casein but the first signs to be noticed are likely to be discolouration or fading, as many dyes are light sensitive.

Although based on protein, casein plastics rarely suffer bio-deterioration although they are not immune from attack by mildew or insects, e.g. moth larvae.

Casein may be washed with cool water containing a small quantity of a mild detergent. CAUTION some casein has been coloured using a surface dye and sometimes this may run, so work carefully and test using a moist white tissue on an inconspicuous part of the object to see if any colour is removed.

After cleaning, casein plastics may be polished using a non-coloured wax polish followed by buffing. The wax can help to insulate the material from changes in humidity. Store or display away from sunlight or bright light. In many respects casein plastics behave like wood and may be stored under similar conditions, i.e. avoid high temperatures and preferably maintain a stable humidity of about 60 percent RH if possible.