The original wood trim and architectural features of your historic house or building are part of its charm and character. The finish on these wood features also contributes to their historic character. Some of your wood features might have an original shellac finish. Shellac was a popular historic wood finish due to its ability to bring out the beauty of wood better than most finishes.

You can determine whether the finish on your woodwork is shellac using denatured alcohol. Place a small amount of denatured alcohol on a rag and wipe an inconspicuous area of the wood. If the finish dissolves, then you know it is shellac. If the finish does not dissolve, then your woodwork has a more modern finish on it. You can purchase denatured alcohol at any paint or hardware store. 

Use of Shellac Finishes

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Interior wood doors were commonly stained and finished with shellac. Source: Bob Yapp

For over 2000 years, shellac was a product of choice for dyes, flooring, woodwork and furniture. Its use as a wood finish flourished in America from the 1600s through the first half of the 20^th century. Most woodwork in historic houses built before 1930 had a shellac finish. Shellac was popular due to its ease of application and repair, fast drying time, quick clean-up, high durability and color control. Shellac comes into two different varieties: amber and clear. Amber is the natural color of shellac; clear shellac has been bleached.

However, by the middle of the 20^th century, most contractors and building owners had switched from shellac finishes to cheap petroleum-based wood varnishes, lacquers and urethanes. If your original shellac finish has been covered with a petroleum-based finish, you cannot easily switch back to a shellac finish. You cannot put a shellac finish over a modern polyurethane finish.

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Other interior wood elements such as shelves were commonly stained and finished with shellac. Source: Bob Yapp

Shellac has been regaining its popularity in recent years. The “green revolution” in construction may be one reason for this surge in popularity. Shellac is considered a “green” product for the following reasons:

• Shellac is the only finish on the market that is all natural and made from a renewable resource. Shellac is made from the hard resin shells created by the Lac bug and deposited on trees in India and Thailand. The resin is processed into flakes and added to denatured alcohol, which comes from crop plants rather than finite petroleum resources.
• Shellac is alcohol-based and meets all federal and state air quality standards.
• Cured shellac is nontoxic.

Blocking Powers of Shellac Finishes

Shellac is still the best wood finish available because it has blocking powers superior to any other finish. These blocking powers include the following:

• Shellac blocks odors like pet urine and smoke better than other products. 
• Shellac blocks the resin from knots and oily exotic woods, preventing them from seeping out and damaging the finish. 
• Shellac blocks silicone contamination. Silicone can cause a fisheye effect that makes it difficult to refinish the wood. Silicone is used in many modern dusting products. The silicone penetrates the wood in small surface cracks that develop over time. Once silicone is in the wood, it is difficult to remove. The only way to remove fisheye is to lightly sand the area and refinish it, then sand again and finish again, repeating the process until the finish is blended to match the non-contaminated areas.

Repairing a Shellac Finish

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Shellac finishes can become cracked. This damage can be repaired by applying denatured alcohol and smoothing out the alligatored shellac finish with a china-bristled brush. Source: Bob Yapp

Shellac is not alcohol- or water stain-resistant, but damage caused by either one can be easily repaired. You can buff out a white water stain on a horizontal surface (such as a tabletop) with a small amount of lemon oil and #0000 steel wool.

You can repair nicks, scratches and marks caused by alcohol by adding more shellac to the damaged area and buffing it with #0000 steel wool. You can buy shellac in premixed cans that has a shelf life of about three years. The more coats of amber shellac you apply, the darker the finish will become. You can control the color by applying amber shellac until you get the color you want, and then adding a clear shellac topcoat over it.

If your shellac surface is “alligatored” with small cracks throughout the finish, it can be repaired. Pour some denatured alcohol into a small can or plastic bucket. Buy a natural bristled brush rated for oil paints and finishes. Dip the brush into the alcohol and allow most of the alcohol drip out of the bristles. Brush the remaining alcohol over the shellac surface. The alcohol will melt the surface of the finish, causing the alligatored finish to smooth out again. When you have restored the old shellac to a smooth consistency, apply a clear shellac topcoat. The finish will look authentic but completely rejuvenated.

Shellac is also very easy to strip. Soak the area you want to strip with denatured alcohol and let it sit for about 30 seconds to soften the finish. Rub the area of softened finish with a medium-grade scouring pads (usually green in color).

Cleaning a Shellac Finish

If your shellac finish is in good condition and just needs cleaning, use a mild, biodegradable liquid dishwashing soap diluted in warm water. Ring the rag out very well before you wipe the shellac surface. Never use "oil soap" products to clean natural historic finishes. These products contain alcohol and will ruin all shellac finishes.

The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.