Today I began refinishing an Engelmann Spruce top or tone board on a uke that looked a little dull, had a lot of minor fingernail marks from playing and had one impact dent toward the bottom. Here is the process.
First I carefully sanded off the old French Polish using dry sandpaper on a perfectly flat and square wooden sanding block. I was especially careful to work exactly to the edges of the saddle and fretboard and to sand until there was none of the shellac color visible on the now bare wood. I started with 220 grit, then 320, then 400 and finally 600. With the exception of the small impact dent it looks great.
The impact dent simply compressed the wood and did not cut it. To raise the wood back you use moisture and heat. I dampened a clean piece of cotton and put it over the dent. I then briefly touch the cloth over the dent with a hot iron. Moisture and heat raised the wood up to its proper level. When the wood dried a little judicious sanding and VOILA, the dent has disappeared.
Now, with a little naptha on a clean cloth I wiped up any remaining sawdust. When the cloth came clean it was time to rub on the first of the "spit coats" of dilute shellac and start the French Polish process. The shellac, diluted with alcohol dries quickly and I was able to get two "spit coats" on this afternoon. I will rub one more on tonight and in the morning will began the polish process with a "munica". The spit coat wants to go on very smoothly as it forms the base of the final finish. Too heavy an application that leaves ridges will result in those same ridges in the final product.