Shellac: The Primitive Polyurethane Finish

by Jonathan Hall

No finish can prevent a wood from hydrating to match the average relative humidity of its climate. The purpose of a finish is to resist water and water-vapor, thus slowing down the moisture exchange that occurs when the relative humidity rises and falls. It is this moisture exchange which stresses wood and causes it to degrade. People today use polyurethane to slow down moisture exchange. Polyurethane is a film finish that resists water and water-vapor very well. Polyurethane is also resistant to abrasion, heat, and solvents. But polyurethane is also carcinogenic, toxic, and smelly.

What if there was an alternative film finish that offered water-vapor resistance superior to polyurethane without the toxicity? A finish that you could apply inside your house and not annoy your loving spouse with smelly fumes? A finish that dried so fast that you could finish a bow in just a few hours? A finish that is natural, nontoxic, and effective? There is such a finish—shellac.

What is shellac? Essentially, it is insect resins dissolved in alcohol. That's right. Insect resins dissolved in alcohol. Shellac is made from the resins secreted by the Lac bug (Laccifera lacca) in India. The female Lac bug feeds off the tree sap and secretes a resin which she uses to incubate her eggs. This resin is scraped from the tree and processed into shellac flakes. These flakes are then dissolved in alcohol and brushed onto the wood, drying into a film finish. The first documented use of shellac as a finish was by an Englishman visiting India circa 1590. Since shellac predates the industrial revolution, I consider it a primitive finish.

Before polyurethane, shellac was used widely as a finish in woodworking. Shellac has been used on children's toys because it dries to a non-toxic finish. Shellac dissolved in pure ethanol has been FDA-approved as a coating for medicines and candy. Shellac is known for its superior adhesion properties over other finishes. Nothing sticks like shellac. Shellac is often used as a sealer coat for oily woods.

Shellac is the original primitive film finish. Shellac rivals and exceeds modern polyurethane in water-vapor resistance, but it is slightly less water resistant than polyurethane. I wouldn't concern myself with this slight lack in water-resistance over polyurethane. It's the water-vapor exchange that stresses wood, and shellac excels in resisting water-vapor. Besides, shellac is more water-resistant than oil, wax, or grease.

The disadvantage to shellac is that it is not as resistant to heat, solvents, or water like polyurethane. Alcohol will dissolve shellac and standing water can discolor the finish. As long as you don't throw your bow in a river or spill whiskey on it, you should be fine. But this disadvantage is also a strong point: shellac is easily repairable. The alcohol in mixed shellac will dissolve and blend the new shellac into the existing finish, resulting in a seamless repair.

Shellac can vary in color from light blonde to dark amber and is either de-waxed or waxed. Waxed shellac flakes have a longer shelf life than de-waxed flakes, but the dewaxed flakes offer a more durable finish. The wax in waxed shellac can prevent other finishes from adhering to the shellac, so it's recommended to use de-waxed shellac as a sealer coat. The only advantage I see to the waxed shellac is a longer shelf life.

Mixing shellac is a fairly straightforward process. Photo 1 shows the necessary materials: denatured alcohol, two ounces of de-waxed super blond shellac, a measuring cup, and a glass mason jar. Do NOT put shellac in a metal container. Shellac is acidic and will react with the metal, resulting in a darkening of the finish. Shellac is measured in "cuts," or the number of pounds of shellac that are cut into a gallon of alcohol. Cuts can vary from 1 to 4 lbs. You won't need to mix up a gallon of shellac unless you are finishing wood floors, or A LOT of bows. I prefer to make eight ounces at a time. I find a 2 lb cut to be good for brushing and general applications.

For a 2 lb cut shellac mix: place two ounces of shellac flakes into the mason jar. Add eight ounces of denatured alcohol and stir with a plastic stick (I use a plastic fork). Place the lid on the jar and give everything a swirl. Place the jar in the refrigerator. You can go back and give the jar a few swirls as the flakes dissolve. It should take no more than two days for the shellac flakes to fully dissolve. If they do not fully dissolve within that time, your shellac may be too old.

Once mixed, shellac begins a process called esterification, wherein the alcohol modifies the shellac resins and eventually turns the shellac into a sticky gum that won't fully dry. This will also happen if your shellac flakes are stored in hot and humid conditions. I strongly suggest you store shellac flakes and mixed shellac in the refrigerator to prolong its lifespan. A good test to see if shellac is still good is to dribble some on a piece of glass that is angled at 45 degrees. Let the shellac dribble down the glass. After drying for fifteen minutes, you should not be able to fingerprint the center of the runoff. In above photo, you can see the shellac flakes are still dissolving. The shellac I mixed was fully dissolved within 48 hours. It is just out of the fridge in photo 3. The jar is a little frosty.

Now that it's mixed, the shellac is ready to use. The thing to remember is that you now have an evaporative finish which will be quite different from oil and polyurethane finishes. Polyurethanes are predominantly oil-based, which is why they take so long to dry and even longer to cure. Polyurethanes and other oilbased finishes are known as curing finishes. Dried polyurethane will emit lingering odors as the finish cures. Shellac is alcohol-based and therefore it is an evaporative finish. Alcohol evaporates quickly, and leaves no odor. You'll find that shellac dries extremely fast compared to polyurethane. You'll have to adjust your application technique.

The key to brushing shellac (and other fast-drying evaporative finishes) is to apply it quickly and brush with light and fast strokes. I've used foam brushes to apply shellac with good results. The alcohol will start to break up the foam brushes pretty quickly, so I prefer to use a bristle brush. The shellac will start drying as soon as it hits the wood, so you have to work quickly. The shellac will dry to tackiness almost instantly and dry thoroughly in about twenty minutes or so. Allow the shellac to dry for two hours before applying a second coat. If the finish feels rough, you can polish it smooth with a few passes of 600 grit sandpaper before applying subsequent coats.

Shellac fumes are minimal. There is the smell of denatured alcohol, and that dissipates in seconds as the shellac dries. After that, there are no lingering fumes. My wife kicks me out of the house when I open a can of polyurethane. She cannot stand the smell of the stuff and complains for days if I have a polyurethaned bow curing inside the house. But shellac is a different story. When shellacking a bow, she stood right next to me and said, "It doesn't smell like anything." Marital harmony achieved.

Shellac will dry to a deep gloss. For your hunting bows, I'd apply a few coats of unbuffed paste wax to give it a matte finish. Wax will also help with abrasion resistance, and I'd recommend it with a hunting bow that will suffer knocks and bumps in the woods. I've been very pleased with shellac as a finish. It is fast-drying, easy to apply, nontoxic, non-carcinogenic, and easily repairable. My wife appreciates the lack of smelly and lingering fumes. Shellac is ideally suited for those looking for a more earthfriendly, safe, and primitive self bow finish.