Process
The process is lengthy and very repetitive. There are also many similar variations in schedule and technique. What is described here is one such schedule. The finish is obtained through a specific combination of different rubbing motions (generally circles and figure-eights), waiting for considerable time, building up layers of polish and then spiriting off any streaks left in the surface.
The pad is first used to put a thinned coat of shellac on, then thicker coats with small amounts of superfine pumice, a crushed volcanic glass. The pumice acts both as a fine abrasive and to fill the pores of open-grain woods. Each coat must be fully dry before the next application, to avoid lifting out the softened finish.
The 'pad' is mostly lubricated with an oil that is integrated into the overall finish. This helps to prevent the 'fad' from lifting previously applied layers of shellac. Typically, "softer" oils, such as mineral oil, will produce a glossier and less durable finish whereas "harder" oils, such as walnut oil and olive oil, will produce a more durable finish.
Additives to the shellac mixture include sandarac (sap of an African cedar) and copal, sap of a South American tree. These and other additives combined with heat and light can make the finish tougher, by cross-linking the polymers and oils in the shellac.
The piece is usually finished off after leveling (1500 grit oil sanding), then light buffing with carnauba paste wax. Too much heat or pressure from buffing will melt off the shellac and result in a bare spot that must be refinished.
Read more about this topic: French Polish
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