Shellac is a natural resin secreted by the female lac bug. It has been used for centuries as a wood finish, electrical insulator, and even a brush-on colorant. But like any natural material, shellac can deteriorate over time when exposed to certain conditions. Understanding what causes shellac to break down can help you prevent damage and extend its usable life.
What is shellac?
Shellac is a resin that comes from the secretions of the female lac bug, which is native to Thailand and India. The lac bug secretes the resin to form a protective cocoon around itself. The coated branches are harvested and the resin is processed to produce shellac flakes, which can then be dissolved in denatured alcohol to create liquid shellac.
Shellac has been used for thousands of years in Asian countries. In Europe and America, its use as a wood finish dates back to the 15th century. Even today it remains popular thanks to its warm tone, natural feel, and ease of application.
Does shellac go bad?
Shellac itself does not spoil or go rancid. Unlike oils and other finishes, shellac does not oxidize or chemically break down over time. As long as the shellac flakes or dissolved shellac liquid is stored properly in an airtight container, it can last for many years without deteriorating.
However, once shellac has been applied as a finish, it can deteriorate due to exposure to sunlight, moisture, alcohol, and abrasion:
Over time, UV radiation from sunlight causes the finish to darken and develop a yellow or amber cast. This is often seen on old shellac finishes on furniture near windows. Darkening happens faster when UV rays are more intense, such as at high altitudes or southern latitudes.
Since shellac is soluble in water, exposure to moisture can cause the finish to soften, whiten, or peel. High humidity or spills can damage shellac finishes. Water rings or white spots are common flaws seen on old shellac-finished furniture.
Pure alcohol can dissolve shellac since that is used to dissolve the flakes into liquid form. Alcohol-containing spills from medicines, perfumes, or cleaning products could interact with the shellac and leave marks.
As a natural resin, shellac is softer and less scratch-resistant than modern synthetic clear coats. Constant rubbing and use can wear through the finish over decades. This is often seen along the edges and handles of old furniture.
So in summary, while pure shellac does not spoil over time, once applied as a finish it can deteriorate from environmental factors like sunlight, moisture, alcohol spills, and physical wear. Proper care is needed to maintain its beauty.
How long does shellac last?
The expected lifespan of a shellac finish depends on several factors:
Quality of application
Properly applied shellac can last decades. Multiple thin coats, lightly sanded between each, will create a more durable film than a single thick application. Brushing on very thin coats avoids trapped air bubbles that can allow premature breakdown.
Use and wear
A shellac finish on a tabletop or other high-use surface will wear faster than one on a decorative shelf. How the finished object is used affects longevity.
Furniture kept indoors in climate-controlled spaces lasts longer than pieces subjected to extreme temperatures, sunlight, and humidity. Avoid placing shellac finishes near heat and sunlight.
Dusting and gently cleaning shellac provides protection by removing abrasive dirt and grime. Touching up worn areas or applying a fresh topcoat before breakdown occurs prolongs the life.
Under ideal conditions – an expertly applied finish, gentle use, and climate-controlled indoor environment – a shellac finish should last 30-50 years with proper maintenance. On surfaces that receive heavy use or abuse, expect shorter service measured in years rather than decades. Outdoors it may only survive one season before requiring renewal.
How to extend shellac’s life
There are several ways you can maximize the lifespan of a shellac finish:
Add a protective topcoat
Applying a thin layer of paste wax, polyurethane, or water-based acrylic over the shellac creates a protective barrier against moisture, spills, and abrasion. This allows the shellac to retain its color and clarity longer. Be sure to test for compatibility first.
Avoid heat and sunlight
Keep shellac-finished items away from direct sun exposure, which degrades the finish more quickly. Similarly, protect the finish from excess heat which can soften the shellac.
Maintain 40-55% relative humidity levels year-round. Low humidity causes wood to dry out and shellac to crack or peel, while high humidity softens the finish. Monitor humidity and use a dehumidifier if needed.
Use a soft cloth for dusting, and clean spills promptly with a damp cloth. Avoid abrasive cleaners, steam, and excess moisture which could scratch or swell the shellac.
Refresh worn areas
Check for wear every few years and use an artist’s brush to re-coat worn sections along edges and handles before they expose bare wood. This prevents moisture intrusion.
Following these tips minimizes damage and renews the protective shellac layer before the wood underneath is compromised. With proper care, the finish can last indefinitely.
Restoring deteriorated shellac
Over time, shellac will naturally darken, feel tacky, or wear unevenly. While some restore the luster with polishing wax, severe deterioration requires more intensive repair:
Use a chemical stripper to fully remove failing, alligatored shellac. Scrape off any gummy residue after the old finish softens. Neutralize stripped wood with denatured alcohol.
Sand down to bare wood using 120-150 grit sandpaper. Finish sanding with 180-220 grit. Be cautious as old shellac can contain lead. Wear a respirator and clean up carefully.
Repair any water damaged areas with a compatible filler. Sand smooth and wipe clean after drying.
Apply multiple new coats of shellac following the original application directions. Use several thin coats for best durability. Consider adding a protective topcoat.
Avoid future deterioration by controlling humidity, avoiding direct sunlight, using coasters and table pads, cleaning carefully, and re-coating annually.
While restoration takes time and care, it can revive a failing shellac finish to a like-new condition. Proper prep work and re-coating technique allow the revived finish to once again last for decades with appropriate maintenance.
Signs shellac is going bad
How can you identify shellac that is no longer in good condition? Here are key signs of deterioration:
Darkening or yellowing
Shellac naturally lightens from an amber color to a clear blond tone as it dries. Darkening, yellowing, or orange staining indicates aging shellac.
Loss of clarity
The resin should dry to a transparent, glossy film. Cloudiness, haziness, or a white haze point to moisture damage or breakdown.
Cracking or peeling
If the finish has shrunk and pulled away from edges or has cracks through multiple layers, the shellac has lost elasticity from age.
The finish should feel dry and solid to the touch. Stickiness, tackiness, or gummy soft areas mean moisture has infiltrated the shellac.
Check for visible wear along edges and handles where hands touch. This shows the protective coating has rubbed off in high-contact areas.
Bare wood peeking through means the shellac has worn through completely in spots, requiring touch ups.
When you notice any of these warning signs, it is time to renew the shellac finish before allowing further deterioration. Addressing issues promptly preserves the wood underneath.
Preventing shellac breakdown
While shellac will eventually require restoration, you can prolong its life span by:
Applying it properly
Ensure proper prep, application in thin coats, and adequate drying time to build up a flexible, durable film.
Using UV-resistant formulas
Shellac formulas containing UV inhibitors better withstand sun exposure without darkening or yellowing prematurely.
Placing furnishings strategically
Avoid placing shellac-finished items in direct sun or near heating vents which dry the wood and finish. Rearranging can help.
Maintaining stable humidity levels
Keep relative humidity between 40-55%. Use dehumidifiers or humidifiers since changes cause movement that stresses the finish.
Cleaning and waxing carefully
Dust with a lint-free cloth and clean spills promptly with minimal moisture. Wax lightly to protect the surface.
Avoiding alcohol damage
Use coasters under glasses and keep perfumes or cleaning products away to prevent disfiguring spots.
While shellac will wear over decades, paying attention to its vulnerabilities allows you to delay restoration and enjoy its warm glow longer.
Frequently Asked Questions
Does shellac expire?
Shellac flakes or pre-mixed liquid shellac does not expire if stored properly in sealed containers. However, once applied as a finish, shellac is susceptible to damage from moisture, sunlight, and wear which reduces its usable life.
Can old shellac be revived?
In many cases, failing shellac finishes can be restored to full strength and luster. Proper techniques for stripping, sanding, and re-coating layers of fresh shellac can revive the finish. Severely damaged sections may need wood repairs.
Should shellac be waxed?
Applying a thin coat of paste wax is recommended to protect the shellac finish from spills, abrasion, and water spotting. Use a wax formulated for antiques and furniture. Avoid silicone polishes which can damage the finish.
How long does shellac last compared to polyurethane?
Polyurethane forms a harder, more scratch-resistant topcoat than shellac. However, it can yellow over time. Under ideal conditions, shellac may last 30-50 years vs. 50-100 years for polyurethane. But shellac is easier to renew when needed.
Can you mix old and new shellac?
It is best to use fresh shellac when restoring a finish. Old shellac may have begun deteriorating, so mixing batches is not recommended. Start with a clean slate by stripping the old finish first.
Although shellac finishes will naturally darken and wear over time, understanding the causes of deterioration allows you to prevent premature damage. With proper humidity control, a protective topcoat, gentle cleaning methods, and periodic restoration, a shellac finish can offer decades of lasting beauty in your home. Handled with care, it can be enjoyed by generations to come.