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How and why to mix fresh shellac
Dan Erlewine shares his experience with shellac
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IN THIS ARTICLE
• Intro from Dan Erlewine
• Advantages & disadvantages of shellac
• Recipe for fresh shellac
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"On the rare occasions that I refinish a guitar, it's usually during a serious structural restoration — in one case a 1958 Gibson ES-5 that was severely burned in a fire — I mix a batch of fresh shellac the day before I start to spray. I don't mix it until all the wood preparation is finished. Our book Finishing Step-By-Step details shellac's desirable qualities. Here are two excerpts from that book — first a description of shellac with its advantages and disadvantages, followed by instructions for mixing fresh shellac (taken from the "recipe" chapter at the end of the book):
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SHELLAC TIP
Speed the shellac dissolving process with warm indirect heat, like from a desk lamp. |
Mixed fresh from flakes, shellac is an excellent sealer under lacquer. It makes a fine finish by itself when applied by French polishing, the preferred technique of many classical guitar makers. Shellac is a favorite in the repair shop as a sealer over repair work, or whenever oils, silicone, and other fisheye-causing contaminants may be present. Shellac can be sprayed, brushed, or rubbed on as a French polish. Every serious builder and repairman should buy some shellac and denatured alcohol (Behkol Solvent, for example) and experiment.
Cuts
The term "cut" is used when referring to the amount of alcohol added to dry shellac flakes to dissolve them (one pound of shellac flakes dissolved in one gallon of alcohol gives a well-thinned one-pound cut). Store-bought shellac is usually sold in a heavier three- to four-pound cut, and then thinned accordingly. (Four pounds of shellac flakes thinned with one gallon of alcohol produce a four-pound-cut shellac.) Common shellac thinning ratios range from a two- to a five-pound cut.
Storage
Once shellac flakes are mixed with alcohol, the mixture has a shelf life of no more than a year and a half. However, most of us discard shellac if it's more than two months old! Keeping it cool will increase mixed shellac's shelf life. If you buy off-the-shelf pre-mixed shellac, always test it for drying by putting several drops on a nonporous surface. Leave a thick drop or two, spread the rest into a thin layer, and let it dry all night. By the next day, the thin layer should be dry and sandable. The thicker drop shouldn't easily take an imprint from your thumbnail. If it does, it may be usable but questionable — give it another day or two of test-drying before using it.
ADVANTAGES & DISADVANTAGES OF SHELLAC
Advantage
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It is an excellent sealer because it sticks to almost anything. It has a golden color and a quality that makes wood look beautiful. It can be brushed, sprayed, or French polished. |
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It blocks out, or seals in, trace amounts of oil, wax, and silicone. |
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It is easily repaired. |
Disadvantages
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Shellac finishes are sensitive to hot objects, and are easily marked by water and alcohol. This isn't necessarily a problem with musical instruments. |
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It must be mixed fresh rather than used straight out of hardware store cans. |
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It is harder to apply than lacquer because it can't be sprayed very thick. Brushing or French polishing shellac is labor intensive. |
RECIPE FOR FRESH SHELLAC
Many finishers keep fresh-mixed shellac on hand for a variety of projects, including French polishing, sealing, wash coating, and touching up. With shellac, fresh is somewhere between two and six months, at which time we throw it out and mix a new (small) batch — a pint or two of shellac in a four-pound cut will go a long way.
Start fresh!
Start with fresh shellac flakes. Here's how you tell. If the flakes are fresh they'll dissolve overnight. If they aren't dissolved in four days, consider discarding your batch and getting new flakes, especially if the mixture doesn't dry when you test it on scrap.
Here's an easy way to mix shellac to the cut we use.
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Into
a clear glass jar with a tight-fitting lid, pour an arbitrary amount of
dry flakes and shake them down so they settle.
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Pour
in denatured alcohol until the flakes are immersed and there's between a
half-inch to an inch of liquid remaining on top the flakes. This produces
a thick shellac in about a four-pound cut that can be thinned as needed
for brushing, French polishing, or spraying.
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Shake
and stir the mixture occasionally to keep it from forming a mound of thick,
undissolved shellac at the bottom of the jar.
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Also,
you can warm it gently, such as with the indirect heat from a desk lamp,
to speed the dissolving process. Our shellac is fresh and will generally
go into solution within four hours if you keep it warm and stir it throughout
that time.
Store shellac, mixed or dry, in a cool dark place.
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Besides
being the best sealer coat, shellac gave the body of this otherwise very
white-looking spruce and maple guitar the golden quality it needed to match
the neck which did not get refinished.
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This
photo represents the true color of the shellac and how it matched the neck's
original finish. The white neck represents exactly how the stripped and
sanded body looked before the shellac was applied.
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I
will use shellac to finish the two sides of the peghead which were burned
beyond saving—just like the tuning keys you see here. The rest of the
fire damaged finish on the neck, including the front and back of the peghead,
I was able to wet-sand and rub out.
— Dan Erlewine |
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This information on shellac is just a sampling of the material covered in Finishing Step-By-Step.
This expanded 2nd edition features color stain mixing charts, a color gallery of vintage finishes, and detailed recipes for recreating them with professional results.
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ColorTone Shellac Flakes
Behlen Behkol Solvent
Guitar Finishing Step-By-Step
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