Copyright© by Gregory Byers.
O. K., here's what's wrong with French polish. It's not as smooth and shiny as glass (usually). It is so thin that it gets scratched just by looking at it. It degrades where it comes in repeated contact with skin and perspiration. It is labor-intensive to apply. Now here's what's right with French polish. It has a warm, non-industrial appearance that is compatible with, and enhances, the organic nature of the underlying wood. It is very thin and, of all the finishes, it gives the most transparent quality to the sound. With time (months to years) it becomes less susceptible to scratching and chemical degradation. It is also very easy to "refresh" and make "new" again, though scratches that have damaged the underlying wood will not be completely eliminated. It also has the merit of being the traditional finish of guitars for hundreds of years. Not least, from my perspective, is that the solvent, alcohol, is relatively benign. I have used water-borne urethane and acrylic lacquers in the past. I can't say I won't use them again, at least on back, sides, and neck, but neither can I say when that might be.
From buildyourguitar.com
This text is not a how-to-do-it description. It's much better to see it than to read about it. I recommend that you watch a demonstration of french polishing on the video Hand-Applied Finishes: Applying Top Coats by Jeff Jewitt (published bywww.taunton.com). This video shows french polishing a table top. The well made video French Polishing for Guitarmakers by Ron Fernández (available from www.fernandezmusic.com orwww.stewmac.com) explains in detail how it is done on the object we are interested in.
French polishing is the quite work-intensive technique of applying shellac with a cloth pad. This very old finishing method gives particularly good results on mahogany, but also on other types of wood.
In French polishing shellac (thinned with denatured alcohol) is applied by moving a pad (made of lint-free cloth) in sequences of circles and figure eights, using a bit of oil as a lubricant. French polishing has a reputation of being very difficult - apparently only experts are capable of doing it. I don't agree. The first time I tried French polishing I was very pleasantly surprised by the results I achieved and watching the gloss slowly develop was a very satisfying experience indeed. To me French polishing is a great and extremely rewarding technique - so why not give it a try?
Dissolve the thin shellac flakes by simply pouring them into alcohol and shaking the solution repeatedly before leaving the flakes to dissolve overnight. Always prepare only the amount that is needed for a particular job as it will not keep very long. A simple test to show whether old shellac can still be used or not is to leave a small drop of the solution to cure overnight; if it doesn't cure but remains gummy, pour it away. Different shellac-alcohol mixtures are commonly used: a mixture of a 1/4 pound of shellac flakes dissolved in 1 pint of alcohol is called a "2-cut" solution.
Shellac is not affected by hand sweat and can withstand temperatures of up to about 80 degrees Celsius (176 degrees Fahrenheit). It is, however, quite easily damaged by alcohol. Surfaces thus damaged are fairly straightforward to repair, though. Avoid using alcohol-based stains under a shellac topcoat as this will cause the stain to be dissolved by the alcohol contained in the shellac mixture, which will lead to patches forming on the surface.
Excerpt from my book Building Electric Guitars
Order the book "Hand-Applied Finishes" by Jeff Jewitt
Keeping brushes in good shape contributes significantly to good finishing results. Often cheap brushes are bought because one assumes that it won't be possible to clean a brush sufficiently well after use anyway. This is, however, a totally wrong assumption. The following instructions for cleaning are intended to give you long-lasting delight with more expensive, good-quality brushes; always carry out all steps of the cleaning process whenever a brush has been used and don't just leave a brush soaked in a solvent-filled container overnight, not even if you intend to continue painting the next day already. Follow these instructions and you will be rewarded with brushes that remain in perfect shape.
First remove any material left on the brush by squeezing it against the walls of the container. Then wash the bristles in a sufficient amount of thinner and, wearing protective gloves, massage them thoroughly with your hands. After this twirl the brush between the palms of your hands so that any solvent left is removed.
Don't worry about using too much solvent for washing the brush: it won't go off and you can use it again later. If you leave it to stand until the solid particles have settled to the bottom of the container, you can pour it through a coffee filter and get fairly clean solvent again for the next time you need some.
After the brush has been thus rough-cleaned, wash it properly in a mixture of plenty of warm water and a bit of hair shampoo by running your fingers through the bristles (commercials will tell you what shampoo to use!). Then wash out the solvent with running water. Repeat and rinse the bristles a second and a third time with fresh water.
Finally, carefully wrap the bristles in paper and put a rubber band or adhesive tape around it to hold the paper in place. This will ensure that the bristles remain straight while the brush is not used.