Generally considered to be the most prestigious and desirable of all the clear finishes, french polish is the best looking, but in many ways the least practical. Its depth and brilliance are unequalled by varnishes or lacquers, because the surface it forms is actually wafer-thin, and gives grain pattern and colour a particular clarity, almost a transparency.
The French Martin brothers developed a polish based on shellac in the eighteenth century, a version of which was being used in England for pianos by 1815. By the late nineteenth century it had become the most popular treatment for high-quality furniture and joinery, especially mahogany. This timber still looks beautiful french polished, but other woods (though not wide-pored oak) can be treated equally successfully.
French polish is resistant to neither heat nor liquids, and is particularly susceptible to alcohol, so table tops are usually waxed to ease maintenance. This is not to say that the finish cannot be repaired at all but rewaxing is a great deal easier and quicker.
There is a certain mystique about polishing, probably because application with a rubber is an involved process, and recognizing the stage it has reached demands experience. Once you have developed a ‘feel’ for the rubber, however, you will find that it is a great deal easier than generations of craftsmen would have us believe. Doing it is really the only way to learn.
If you are finishing a new piece there is very little to be said for french polishing it, if it will be getting ordinary household use. But you will find it on antique, old or reproduction furniture and will need to know how to apply it when you are refinishing.
French polish is particularly reactive to damp; white blotches will appear in the finish if you apply it in & humid atmosphere, and it will not harden if the temperature in your workspace is less than 15°C (60°F). If conditions are bad and you still have to french polish, fix up a non-flammable heater over the surface, or warm it over with an iron on top of a blanket. This can also eliminate damp patches in the wood fibres.
Shellac
The basic ingredients of french polish are shellac and methylated spirits (wood alcohol). The secretions from the lac insect, found in India, Africa and the Far East, were originally used for red dye; while commercial chemistry has evolved better and cheaper colouring agents, there is still no synthetic equivalent of lac for french polish. The fluids secreted from the larvae encrust the twigs of infested trees; the ‘stick lac’ formed like this is harvested, pounded, melted, refined and filtered through ‘seed’ and ‘lump’ stages to make wafer-thin sheets. These sheets are then flaked and exported as shellac.