French Polishing

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What Is French Polishing?

The term French Polishing refers to the art of using what is know as a pad, rubber, or muneca constructed usually of cotton cloth wrapped around some type of core material to apply a finish to a wood surface by rubbing.  So the term French polishing is really talking about the physical act and technique of applying the finish rather that the type of finish itself.

The most traditional french polished surface is different from what we typically do on guitars today. The original craftsmen doing french polishing on furniture would simply fill the pours of the wood and leave only a slight coating of varnish on the surface of the wood.

Today professional French polishers will usually build the finish on top of the surface more in order to give it a high gloss look and to increase durability. Even with a slightly heavier build a French Polish finish is usually far thinner than any synthetic type of sprayed or brushed finish.

The Shellac Finish

The most commonly used material to be applied with the French polishing technique is shellac. Shellac is a natural resin that is made by the Lac Beetle when it feeds on the sap of several different types of trees in India and Southeast Asia. The Lac beetle forms a shell in which it will lay eggs which is made of Lac.  The process of harvesting and collecting lac begins as the trees are infested with lac beetles who build their shells on the branches of the tree which is then scraped off with a hot knife and collected.

The rough material collected for the initial harvest is called stick lac, because it contains a lot of sticks and dirt, dead bug bodies, etc. The stick lac is then refined in a number of ways; It can go to a factory for industrial processing to be carried out in order to purify it into the final thin flakes that it will be sold in for various commercial and other uses.

The stick lac can also be purified by hand by initially being roughly filtered into what we know as seed lac. As you might guess by the name,the seed lac form resembles tiny seeds of resin. At this stage there is still a good amount of wood chips and bugs in there, but it is usable for French polishing after being dissolved and filtered for use.

The next stage in handmade shellac is to take the seed lac and fill long cotton bags with it. Then the bags are held over a fire to be heated and the hot shellac is squeezed through the fibers of the cloth bag dropping large drops of shellac onto the ground that resemble large buttons. I have read in other places that the buttons may also be made by  scooping it out with a spatula onto a plate and then reheating it again to smooth the surface.  This type of shellac is know as “button lac”. 

Button lac is my personal favorite type of shellac to use because it is in a very raw and un-tampered with state. But most importantly , because it was heated more, it forms a tougher more impact resistant coating due to the resulting polymerization that occurs from the heating process.

Using other hand methods the resin can also be dissolved in alcohol , filtered, and them poured out onto huge pans to dry letting the solvent escape. It can even be stretched out into a thin sheet while still hot which is common in hand made shellac production. Once the thin sheet of shellac resin has hardened it can be shattered and broken into the flakes we commonly see when purchasing flak shellac.

Today most commonly the flake shellac is commercially produced in factories using a variety of different methods for dissolving and filtering, some of which compromise the gloss, durability, and purity of the final flake shellac. I try not to use any commercially produced shellac if possible.

Shellac Colors

The stunning and unique color of different shellacs are a result of several different factors. One of the contributing factors in producing the many beautiful colors of shellac is the season in which the shellac was harvested. A summer shellac, known as Bysakhi will be a very dark and intense color while the winter harvest called Kusmi will be more caramel colored and much lighter.

It is very sad to me that with the amazing verity of shellacs available, I rarely see people using the darker shades of shellac. I feel that for the guitar maker it is essential to use the darker colors of shellac. Using at least some color will unify the instrument and help it to look like a complete object rather than a bunch of parts put together.

It is really not that hard to use darker colors, once you get your technique mastered to the point that you are applying a very even coat of finish on the guitar. There are some guidelines that should be followed though, to ensure that your guitar will look as beautiful as possible with a darker colored shellac finish.

Types Of Alcohol For Making Shellac

Now that we have talked a little bit about the resin and what it is, we can talk about the other main component of our finish which is alcohol. There are several different types of alcohol that can be used for french polishing with shellac, and each type will produce different results.

Many people choose the type of alcohol they use for french polishing based on which one is the cheapest, but what they don’t realize is that to do so might be compromising the look of their finish, let me explain why.

Each type of alcohol and even different brands of the same type of alcohol will have different effects on the shellac resin. The most striking difference is in color. If you start with a nice Kusmi button lac and dissolve it in denatured alcohol you will get a very yellow and week looking color that lacks fire. If you mix the same Kusmi button shellac with some pure ethanol like Everclear, the color will be very warm, full of fire, and wonderful red hues. I also find that using pure ethanol will give you much better chances of getting a dichroic effect in your finish which is what I’m after. The dichroism present in some shellacs give the finish a fire similar to a natural diamond or gemstone and makes any synthetic finish look dead and unnatural when compared side by side.

Oils Used For French Polishing

The final important component in the formula for a beautiful and durable French Polished shellac finish is oil. The most commonly used oil is probably olive oil. The second would be mineral oil, followed by walnut oil.

Different oils have different properties they bring to the finish during application as well as the long term properties of the finish itself. There are two basic types of oils: drying oils and non drying oils. A non drying oil will not polymerize and will remain somewhat fluid and continue to migrate indefinitely. Olive oil and mineral oil are in this category of non drying oils. The non drying oils are great for use in facilitating the application of the shellac with a pad via the French Polishing technique. A small amount of these can be added directly to the pad in order to increase the lubrication between the pad and the finished surface, enabling the finisher to apply more finish and with a smoother texture.

The drying oils such as Walnut oil will fully polymerize and become a permanent part of the finish itself. The function of this type of oil is two fold:

  1. To add flexibility to the finish and act as a plasticizer in the formula of our shellac and alcohol mixture. This will help the finish to move with the wood as well and prevent checking.
  2. Increase the gloss of the finish and enable the finisher to get a rich and lustrous sheen that will not dull and flatten like a shellac finish without a drying oil.

An added bonus of using walnut oil as a plasticizer is that once it fully polymerizes, there will be an increase in solvent resistance due to the fact that the polymerized walnut oil component of the finish has no solvent.

Different finishers have personal preferences in using different types of oils. I use several different oils throughout the French Polishing process for specific purposes aimed at  producing the highest quality, most beautiful, and best sounding finish possible.

Guitar French Polishing Technique

The traditional technique of French polishing refers to the way that the shellac finish is applied to the guitar. This is most commonly done with a cotton cloth, usually with some type of core material inside. The quality of the finish is completely dependent on the proper technique being used to apply it. It takes years of practice to fully master this and if approached correctly, can be an incredibly enriching experience as it was for me. Mastering the French polishing technique forces one to develop control, strength, and patience.

One of the reasons I love to teach French polishing, is because I feel that it embodies the heart of the traditional craft of lutherie.  Through learning and mastering it, the luthier will raise the quality of his or her instruments and the quality of their time in the workshop as they begin to view the work thorough the unique lens of their newly acquired skill set and sensitivities.

When I learned this ancient art from my teacher Eugene Clark, it not only helped me to make my guitars sound noticeably better and look more beautiful, but it also raised my awareness of my body as pertaining to my technique in all the tasks that I perform as I create my guitars. Mastering the art of french polishing involves mastering your body and mind, and spills over into every area of your life. Looking back I can say that mastering the French Polishing technique was one of the hardest things I have ever done, and also one of the most beneficial, enriching, and rewarding as well.

Learn How To French Polish A Guitar Online:
The Art OF French Polishing

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