Shellac: A Challenging Finish

Many choices. There are a lot of shellacs from which to choose. In liquid form there is (from left) clear shellac with the wax removed, clear with wax, and amber with wax. In flake form you can choose from (from left) superblonde, lemon yellow, orange, garnet and extra dark.

This traditional finish can be tricky to apply.

If you have read much in the woodworking press, you’ve surely encountered many articles, including mine, in which the writer uses and recommends shellac as a finish. This may persuade you to try shellac.

I certainly don’t want to discourage you because shellac is a great finish with a great history. But you need to be aware that shellac is a relatively difficult finish to use. The writers recommending shellac are usually advanced woodworkers who have learned to overcome the difficulties.

By pointing out some of the problems, I hope to increase your likelihood of success.

Name Confusion

Before you even get started, you have to overcome the confused naming of shellac and the large variety of shellacs available in flake form.

In liquid form, there are clear (actually pale yellow) and amber shellacs. Until about 20 years ago, when the sole remaining supplier, Zinsser, changed the names for marketing purposes, these were labeled “white” and “orange.” “Who wants orange furniture?” was the explanation.

In solid flake form, which you dissolve yourself in denatured alcohol, the names include: blonde, superblonde, lemon yellow, orange, garnet, button, ruby, extra dark and more. These names all refer to the color, ranging from pale yellow to very dark orange.

Where to start? Usually clear or blonde on light woods and anything on dark or dark-stained woods. Whichever you choose, it’s not as simple as buying a can of polyurethane at a home center.

Wax or No Wax

There’s also the issue of wax. Shellac is a natural resin secreted from insects that feed off of plum trees in South Asia. This resin naturally contains 4 to 5 percent wax.

The wax can inhibit bonding with other finishes, so Zinsser introduced a dewaxed shellac called “SealCoat” and markets it as a sealer for polyurethane – even though polyurethane, like all finishes, seals perfectly well on its own. (As I’ve written many times, the need to use shellac as a sealer is way overblown except for some refinishing situations.)

Clear and amber liquid shellacs still contain the wax. Most varieties of flake shellac have the wax removed. There’s no noticeable difference when you use the shellac for the entire finish.

Pound Cut

Unlike other finishes, in which all brands within a category have similar solids content (the ratio of the finish that hardens to the total liquid, including solvent), liquid shellac can vary from almost no solids to very high solids depending on the ratio of shellac flakes dissolved.

The system used to measure the relative solids content is called “pound cut,” which is the ratio of the number of pounds of shellac flakes dissolved in one gallon of alcohol.

Clear and amber liquid shellacs are 3-pound cut (too thick for brushing without brush marks, so you need to add thinner). SealCoat is 2-pound cut (at the upper limit for easy brushing). When you dissolve your own shellac flakes, you determine the pound cut.

You don’t have to deal with these variations using any other finish.

No Satin

Shellac is the only film-building finish not available in sheens ranging from gloss to flat. All shellacs are high gloss.

If you want a satin sheen, you have to rub the shellac with fine steel wool or other abrasive. This is more work, and it creates fine scratches that make the surface very fragile. Any slight abrasion, even a light pass with the back of your fingernail, will level the ridges between the scratches and leave a mark.

To reduce marking, you can apply paste wax or a silicone furniture polish. Both raise the shine back to a soft gloss, but applying paste wax is a lot of work.

Blushing

Just like lacquer, shellac blushes (turns milky white) in warm, humid conditions. Unlike lacquer, there aren’t widely available solvents for handling this problem.

Blushing. Like lacquer, shellac blushes in humid conditions. You can see the blushing developing in the lower half of this panel that I just brushed. Sometimes the blushing disappears on its own. Otherwise, wait for a drier day or add lacquer retarder to the shellac.

With lacquer, you can add lacquer retarder to eliminate the blushing (though this slows the drying). You can add lacquer retarder to shellac also, and this is the best solution for the problem (other than waiting for a drier day). But try it on scrap wood first because lacquer retarders are formulated differently and the shellac may not dry properly.

Finishes other than shellac and lacquer don’t blush.

Ridging

Unlike other finishes, shellac tends to ridge at the edges of brush strokes. The way to reduce the ridging is to add more thinner, but then you have to apply more coats to get the same film thickness.

Ridging. Unlike other finishes, shellac tends to ridge at the edges of brush strokes, as shown here on soft maple. This is the color produced by one brush stroke of 2-pound-cut garnet shellac.

Shelf Life

The biggest problem with shellac is probably shelf life. Shellac is unique in that it deteriorates – especially in liquid form, but also in flake form.

In flake form, shellac usually stays good for many years unless it is stored in hot conditions or has been bleached to create a “blonde” color. When the flakes go bad, they usually (but not always) “block” into a solid lump, and they no longer dissolve well in alcohol.

Blocking. A good indicator, especially with bleached flake shellac, that the shellac won’t dissolve is “blocking” – the flakes and powder lump into a solid. You can always try it, but this shellac is probably no good.

In liquid form, the deterioration begins immediately upon dissolving. If the shellac is stored in cool conditions, you won’t notice any difference for six months or so. But in time you’ll notice that the shellac dries more slowly, takes much longer to harden and becomes susceptible to watermarking (freshly dissolved shellac doesn’t watermark except in contact with very hot water).

Zinsser used to stamp the date of “dissolving” on their cans, which was helpful in letting you know the age of the shellac. Now the company just stamps a lot number, which is of no help.

Shelf life. If flakes won’t dissolve after a day or two, the shellac is no good and should be thrown out. Shellac is somewhat unpredictable because it is a natural material. The orange flakes I tried to dissolve here looked perfectly good; they weren’t “blocked.” But they still wouldn’t dissolve.

Short shelf life is the reason advanced woodworkers usually dissolve their own shellac from flakes. Freshly dissolved shellac always performs better.

Dissolving Your Own

Even dissolving your own shellac can be problematic. It’s extra work, of course, and you have to plan in advance so the shellac is ready when you are. You also have to weigh the flakes and figure the proportions to get the pound cut you want.

You should stir the dissolving flakes often. Merely shaking the container now and then will result in a hard lump of gummy shellac at the bottom that will be difficult to stir in.

No matter how you cut it, shellac is a relatively difficult finish.