The dissolved shellac is applied, using pure natural oil as a lubricant.
Shellac is an animal product. It is found on some specific trees in the forests of India and other far Eastern countries. Swarms of tiny insects, known as the Lac insect (coccus Lacca) living in these trees, produce, after feeding, through their pores a gummy substance that hardens into a protective covering called lac. The twigs and bark containing the gum or l
ac, are broken off from the trees and crushed in primitive stone mills to separate the gum from the wood. After sifting the gum, they are washed in large tubs of warm water and dried over charcoal fire in cotton bags. When the gum or lac starts to melt, the bags are squeezed to force the gum to the outside of the bags. Next the gum is scraped off by hand and the gum shells (or shell lac) are put on heated thin sheets where it can congeal. When this occurs, the shell-lac is broken into flakes with a knife, forming the dry shellac flakes that we use to make French polish. Over a period of years the term "shell lac" has become known as "shellac."
Shellac color variations are made by bleaching processes. There are white, blonde, orange and dark shellac flake colors. By dissolving shellac flakes in denatured alcohol or ethanol 98% we get shellac varnish. Most luthiers have their own, personal shellac mixing system, kind of secret recipe of the master guitar maker adding different types of resins and hardners. Some use shellac varnish having a short shelf life of about 6 months facing chemical degradation and alcohol evaporation, other luthiers use shellac mixtures that has been made years ago. It is advisable not to use pre-mixed, canned shellac since they contain a number of additives, designed to extend shelf life and to adapt drying times, that are not suitable for French polishing.
Generally, a 2 pound cut is enough to French polish an entire guitar. A 2 pound cut shellac can be made by dissolving 60 grams (2 ounces) of shellac flakes into 240 milliliters (8 ounces) of denatured alcohol. After 3 days the shellac flakes are dissolved. To speed this process, once can put the mixture in hot water bath. Once dissolved, the shellac is to be transferred to the squeeze bottle.
Since very severe skills and experience is needed to apply shellac finishes, every guitar maker will apply his shellac in a little different way. Before applying shellac finish, the flamenco guitar needs to be well scraped, sanded and all gaps, pores and grains need to be filled, using very fine pore filler or pumice particles. The dissolved shellac is applied, using pure walnut, paraffin or sumatra oil as a lubricant.
The French polish process begins with the application of a thin wash coat to the whole instrument. To apply this first base coat, sealing the flamenco guitar, saturate a corner of the folded cloth pad until thoroughly wet, then apply a drop of oil to the same area. The shellac will be applied by pressing the muneca or rubbing pad (a folded piece of an old t-shirt) firmly against the wood dispensing the shellac properly. Next, drag the cloth pad over the purfling and bindings, following the contour of the flamenco guitar, in a single pass without stopping, with no side-to-side movements and quickly to avoid that colors being left in the inlays. In circular motions, wipe the unfinished areas of the flamenco guitar wood surfaces. A firm pressure is necessary to bound the new applied layer of shellac with the previous layer, eventually evolving into a hard, seemingly deep finish. If needed, the use of oil is required to prevent the muneca from sticking against the wood.
Next step in the French polish process is only required for a negra flamenco guitar. Porous woods like rosewood, need to have their pores filled. To do so, add about 10 to 12 drops of alcohol to a new muneca and a small portion of pumice. Be careful never to apply pumice directly to the surface of the flamenco guitar. Pumice may seem an unlikely filler since it is a powdered, white stone. However when suspended in alcohol it becomes transparent, absorbing wood colors when it is rubbed into the grains. Pumice behaves itself like lightweight powdered glass, hardening the wood surface. Partly, this effect is responsible for the clear sound of a French polished flamenco guitar, influencing the instrument its resonance. Pumice or other fillers are never to be used on spruce of cedar soundboard woods, nor on less porous guitar body woods like cypress. These woods obtain a beautiful French polish finish without the use of any fillers.
Now we start applying shellac in as many thin microscopically applications as needed until the desired finish is achieved. To do so, glide the shellac-oil based muneca onto the surface of the guitar, using circular or figure-eight strokes. Never stop moving the muneca when it is in contact with the woods of the flamenco guitar. Once a shellac layer has been applied, the guitar should be left to gas out and dry for several hours between each layer. So the work is done in sessions of about an hour, maybe three sessions in a day, taking about one week in total. In between each layer, the excess oil has to be removed with only alcohol on the muneca as a preparation for the next shellac layer.
When all shellac layers have been applied, we move to the glazing step of French polishing using a very thin cut of shellac. At the moment when the final glaze coats are dry, which takes about 2 weeks, we are ready to polish out the guitar with an abrasives and silicone free polisher. Last step is the easiest one, preserve the French polished guitar and let it cured for about four weeks.