Shellac is a natural resin derived from the secretions of a bug. It has been used in food preparation, electrical insulation, watchmaking, archery, bicycle-making… in fact this remarkable substance is one of the most important natural products that most people have never heard of.
The use of shellac dates back to ancient times. Historical records suggest that it was used in India as early as 1500 BC. By the 17th century, shellac made its way to Europe, where it gained popularity as a wood finish and a key ingredient in varnishes and polishes. It continues to be valued in woodworking for its versatility and aesthetic appeal.
During the 19th and early 20th centuries, shellac was one of the primary finishes used in woodworking. It was prized for its quick drying time, high gloss finish, and excellent workability. However, with the advent of synthetic finishes and lacquers in the mid-20th century, shellac's popularity waned. Despite this, it remains a preferred choice for many woodworkers, especially those involved in restoration and fine furniture making.
Where Does Shellac Come From?
Shellac originates from the forests of India and Thailand. The tiny lac bug (Kerria lacca) resides feeds on tree sap and excretes a resinous substance that it uses to form a protective covering. So much resin is produced that it makes thick crusts on the branches, and it is this crust that forms the raw material for shellac production.
A branch encrusted with lac resin
Between 50,000 and 300,000 lac bugs are required to produce 1 kilogram of shellac.
The raw shellac is scraped from the branches and contains bark shavings and lac bugs. It is melted and filtered through canvas bags The thick, sticky shellac is then dried into a flat sheet and broken into flakes, or dried into buttons.
How is Shellac Prepared for Wood Finishing?
Shellac dissolves readily in ethanol, producing what is known as a ‘spirit varnish’. Unlike oil varnishes which dry by polymerising over hours or days, spirit varnishes dry in minutes or even seconds by the evaporation of the solvent, leaving a film of the solid component behind.
The concentration of shellac is traditionally measured by the unit "pound cut", referring to the weight in pounds of shellac flakes per gallon of alcohol. A one-pound cut of shellac is one pound of shellac flakes dissolved in a gallon of alcohol - equivalent to 120 grams per litre.
While dry shellac can be bought and mixed by the user, pre-dissolved shellac is also available. This has a shelf life, so always check that it is useable by putting a small amount on a smooth surface, if it dries to a film in less than 20 minutes, the shellac is still good.
Shellac naturally contains a small amount of wax. Dewaxed shellac is preferred for applications where it will be coated with something else, such as paint or varnish, so that the topcoat will adhere. However, the wax is beneficial in most other applications, and is used in concentrated form by woodturners for friction polishes.
The Pros of Using Shellac
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Natural and Non-toxic: Shellac is an all-natural product, making it an environmentally friendly choice. It is non-toxic when dry, making it safe for use on children's furniture and items that come into contact with food, such as cutting boards and wooden utensils.
- Ease of Application: One of shellac’s most appealing features is its ease of application. It can be brushed, padded, or sprayed onto wood surfaces. Shellac dries quickly, often within 30 minutes to an hour, allowing for multiple coats to be applied in a single day.
- Beautiful Finish: Shellac imparts a warm, rich glow to wood, enhancing its natural beauty. It is available in various shades, from clear to deep amber, allowing woodworkers to achieve different looks. The finish can be built up to a high gloss or rubbed down to a soft sheen, providing versatility in the final appearance.
- Repairability: Unlike many modern finishes, shellac is easily repairable. Damaged or worn areas can be re-dissolved with alcohol and blended seamlessly with the surrounding finish. This property makes shellac an excellent choice for antiques and high-quality furniture that may require touch-ups over time.
- Compatibility: Shellac can be used as a sealer or primer under other finishes, including polyurethane, varnish, and lacquer. This makes it a versatile component in various finishing systems.
The Cons of Using Shellac
- Water Sensitivity: Shellac’s primary drawback is its susceptibility to water. Prolonged exposure to moisture can cause white rings or spots to form on the surface. For this reason, shellac is not ideal for surfaces that are frequently exposed to water, such as kitchen countertops and bathroom fixtures.
- Alcohol Sensitivity: Because shellac is dissolved in alcohol, it remains sensitive to alcohol spills even after it has dried. This can lead to damage if alcoholic beverages or cleaning products come into contact with the finish.
- Limited Durability: While shellac provides a beautiful finish, it is not as durable as some modern synthetic finishes. It is more prone to scratches and wear, making it less suitable for high-traffic or heavily used furniture.
- Storage and Shelf Life: Shellac has a limited shelf life once it is dissolved in alcohol. The solution can degrade over time, leading to a less effective finish. Woodworkers need to mix fresh batches regularly or purchase pre-mixed shellac with a known shelf life.
- Application Conditions: Shellac application requires some care regarding environmental conditions. High humidity can cause the finish to blush or become cloudy, while very dry conditions can make it challenging to apply smoothly.
Despite its limitations, shellac remains a beloved finish in woodworking for its ease of use, repairability, and beautiful results. Its historical significance and natural origins add to its charm, making it a timeless choice for those who appreciate the art and tradition of woodworking. Whether used alone or in combination with other finishes, shellac continues to hold a special place in the hearts of woodworkers who value its unique qualities.