Wiki

French Polishing

French polishing is a wood finishing technique that results in a very high gloss surface, with a deep colour and chatoyancy. Shellac is the purified secretion of the lac beetle, a sap-sucking insect from India and Thailand. It can be bought ready mixed, or in flakes or "buttons" and may be clear or tinted red (ruby) golden, (blonde) or other colors. French polishing consists of applying many thin coats of shellac dissolved in alcohol using a rubbing pad. The rubbing pad is made up of absorbent cotton or wool cloth wadding inside a square piece of fabric (usually soft cotton cloth) and is commonly referred to as a fad.

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 finish is considered to be one of the most beautiful ways to finish highly figured wood, but it is also recognised to be fragile. It is softer than modern varnishes and lacquers and is particularly sensitive to spills of water or alcohol, which often produce white cloudy marks. However it is also simpler to repair than a damaged varnish finish, as patch repairs to French polish may be easily blended into an existing finish.

"French polish" is a process, not a material. The main material is shellac, although there are several other shellac-based finishes, not all of which class as French polishing.

The process is lengthy and very repetitive. 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 'fad' is commonly 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.

French polishing became prominent in the 18th century. In the Victorian era, French polishing was commonly used on mahogany and other expensive woods, and was considered the best possible finish for fine furniture and string instruments such as pianos, lutes and guitars. The process was very labour intensive, however, and many major manufacturers abandoned the technique around 1930, preferring the cheaper and quicker techniques of spray finishing nitrocellulose lacquer and abrasive buffing. In Britain, instead of abrasive buffing, a fad of "pullover" is used in much the same way as traditional French polishing. This slightly melts the sprayed surface and has the effect of filling the grain and burnishing at the same time to leave a "French polished" look.

Another reason shellac fell from favour is its tendency to melt under low heat; for example, hot cups can leave marks on it. However, French polish is far more forgiving than any other finish in the sense that unlike lacquers, it can be easily repaired.