French polishing with shellac has long been the finish of choice for quality guitars, Not only does it have great beauty, but it can also be applied very thinly, thus having minimal influence on the sound.
However, shellac can be a delicate finish, and unless treated with considerable care, can start to look scruffy fairly quickly. Alcohol must be kept well away, and sweat can also affect the finish quite badly. On the plus side, it is one of the easiest finishes to repair or refurbish. Typically, a shellac finish will need a touch up every couple of years.
Oil is a relatively hard-wearing finish which is steadily becoming more popular on quality guitars. Properly applied, it gives a beautiful ‘in the wood’ appearance prized by top furniture makers.
The Oils used for guitar finishes are actually oil/varnish mixtures, and the amount of solids determines the lustre which can be obtained – anything from matt to a mirror gloss.
Producing a good quality oil finish can take longer than french polishing, due to the increased drying times.