The Case for Shellac
Today, shellac is the most under-appreciated of all finishes, but this hasn’t always been the case. Until the 1920s, when lacquer was introduced, shellac was the primary finish used in furniture factories and small woodworking shops. It continued to be the favored finish of professionals finishing interior wood trim and floors, and of hobbyists finishing everything, including furniture, until the 1950s and 60s.
Then polyurethane and “wiping” varnish (varnish thinned about half with paint thinner and often mislabeled “tung oil”) were introduced and widely promoted. Beginning in the 1970s, blends of linseed oil and varnish, like Watco Danish Oil, were promoted in magazines for their ease of use.
Instead of defending shellac during this period, suppliers retreated to the position that shellac was a good sealer for stains and knots. They also allowed shellac to get an exaggerated reputation for weak water resistance, and they increased its stated “shelf life” from one year to three years. (Shellac slowly deteriorates after it’s dissolved in alcohol. After about a year it no longer hardens well enough or is water-resistant enough to be used as a complete finish on most furniture and cabinet surfaces. Always use shellac within a year of when it was dissolved.)
Now shellac is rarely used as a finish except by high-end antique refinishers (which ought to tell you something). This is terribly unfortunate, because shellac still is one of the best finish choices for most woodworking and refinishing projects.
What is Shellac?
Shellac is a natural resin secreted by insects called lac bugs, which attach themselves to certain trees native to India and Southeast Asia. Suppliers buy the resin and sell it as flakes, or dissolve it in alcohol and package the solution in cans for you to purchase.
Natural shellac is orange (amber) in color and is your best choice when you want to add warmth to wood. Most old furniture and woodwork was finished with orange shellac. Bleached shellac (sold as “white” or “clear”) is best when you want to maintain the whiteness of a pickling stain or the natural color of light woods such as maple, birch and poplar. You can mix orange and bleached shellac to achieve an in-between color.
Natural shellac contains about 5 percent wax and will produce excellent results; but dewaxed shellac, whether pre-dissolved or in flake form, is more water-resistant. You can remove wax from regular shellac by letting it settle and then decanting the liquid.
Shellac is a very old finish, so it has an old measuring system based on the concept of “pound cut.” One pound of shellac flakes dissolved in one gallon of alcohol equals a one-pound cut. Two pounds in one gallon is a two-pound cut; one pound in a quart is a four-pound cut; and so on.
The shellac you buy at the paint store is almost always a three-pound cut, which is very thick for brushing or spraying. Thin this shellac by half with denatured alcohol (shellac thinner) and make adjustments from there to reach the thickness, or pound cut, you feel most comfortable working with.
To obtain maximum freshness and thus maximum hardness and water resistance, use denatured alcohol to dissolve your own shellac from flakes, which are available from many woodworking suppliers. Start with a two-pound cut, and adjust from there.