French Polishing is a process, not a material. The material used when French Polishing is called shellac, which is a resin secreted by the female Lac beetle to form a cocoon in trees in India and Thailand. The colour of shellac varies with the type of tree the Lac insect was living on, ranging from a deep garnet through orange to pale yellow. It is dried into flakes and then diluted into alcohol to make a liquid shellac. Shellac was confined to the Far East until traders introduced it to Europe in the 1700s, it wasn't until the 18th century that the technique was refined by the French.
Furniture from the Georgian and Regency era and most certainly Victorian furniture will have been French Polished or sealed with a shellac.
The purpose of finishing with shellac is primarily for appearance and protection. Wooden furniture needs to be protected against conditions such as humidity, sunlight and everyday wear and tear such as water marks. Shellac also enhances the appearance of the timber and this is where French Polishing comes into its own, the rich colour and distinctive figuring of the grain in the wood is brought to life, leaving the wood with a beautiful lustre and sheen. The process can also be used to change the colour of the timber, hide blemishes, repair damaged surfaces and dramatically improve the appearance of a plain piece of furniture or fixture. Although less durable than a modern lacquered finish, French polish is far more forgiving than any other finish in the sense that unlike lacquers, it can be efficiently repaired.
Polish is applied as a liquid mixture by either polish mop, usually made from bear or squirrel hair, or by a polish rubber which is made up of wadding wrapped in cotton.
Once spread over a surface, the shellac forms a thin, solid coating. The changeover from a liquid that is relatively easy to apply, to a tough, well adhering film, is accomplished by the solvent simply evaporating and leaving behind its solid component as the film coating.
The French polisher applies the first coats by polish mop in the direction of the grain, the surface is then sanded down with a very fine abrasive paper to ensure the surface remains smooth and to prepare the surface for application with the polish rubber. The polish rubber is moved across the surface in the direction of the grain starting with small figure of eight movements from the centre outwards. The pressure is gradually increased as the rubber applies the shellac to the surface. This process is repeated many times.
As every new, extremely thin coat of shellac is applied, it's alcohol solvent melts the uppermost part of the hardened shellac film already on the furniture. This makes for excellent bonding between coats.
The ultimate goal of French polish is to achieve layer upon layer of shellac that fills in all the woods pores and eventually reaches the point where a thin, perfectly flat film covers the entire surface of the piece.
Dark, fine grained woods such as Mahogany, Walnut and Rosewood benefit the most from French polishing. Not all wood types require such a lengthy process for finishing. Oak for example which is a rustic and coarse grained timber, is best left unfilled. Pine and Teak however prefer a low lustre finish, which is achieved using waxes and oils.