Temperature problems with French polishing in restoration work
French polishing produces a very fine finish on wood and before spray techniques this was the method used for fine furniture.
French polish is made from dry shellac* flakes dissolved in methelated spirits (alcohol). Gum sandarac** is added to this which gives the finish a little extra elasticity and resistance to scratches.
The applicator or rubber is made from old cotton wool into a manageable size and then wrapped inside another piece of opened weave cotton cloth.
All polishing whether French or sprayed synthetics and even gluing is affected by the temperature. This poses a problem with the polishing process as each pass of the rubbing cloth over the wood leaves a thin layer of polish and in cold weather the alcohol in the mixture does not evaporate and in some instances may leave a white film.
The polishing must be done in more favourably warm conditions not only the temperature of the room but also the wood surface itself must be warm and to this end sometimes I have to bring small pieces home if the temperature in the workshop is too cold. The ideal temperature range is around 20°C to 24°C.
When restoring old pieces of furniture French polishing is the only method that should be used as the authenticity of a valued piece must be preserved.
French polishing is very time consuming as the rubber has to be passed over the piece many times in order to build up the finish and a small box for instance can take many hours of rubbing.
Shellac French polish is much more delicate and easily damaged than the modern lacquers or synthetic finishes but it is more easily repaired as patches can be worked whereas with the spray synthetic finishes the whole piece must be sanded back and re-sprayed.
*Shellac is resin secreted by the female lac bug on trees in the forests of India and Thailand. It is processed and sold as dry flakes.
**Sandarac, is a resin obtained from a small coniferous tree