Before the advent of modern spray-on one-coat varnish, hand-padded shellac-based finishes were used to create a flawless, aqueous gloss. As you can guess, today's discussion about wood finishes is designated to Shellac, which is the most underrated of all finishes.
Shellac (/ʃəˈlæk/) is a resin secreted by the female lac bug on trees in the forests of India and Thailand. (The word lac means "one hundred thousand," referring to the number of insects found on a single branch. Approximately 1.5 million bugs must be harvested to make 1 pound of shellac.) The resin is scraped from the twigs and branches of the trees. It's then melted, strained to remove bug parts and other foreign matter, and formed into large thin sheets that are broken up into flakes sheets. Those sheets are processed and sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze, and wood finish. Shellac functions as a tough natural primer, sanding sealant, tannin-blocker, odor-blocker, stain, and high-gloss varnish. Shellac was once used in electrical applications as it possesses good insulation qualities and it seals out moisture. Phonograph and 78 rpm gramophone records were made of it until they were replaced by vinyl long-playing records from the 1950s onwards.
It is well known for its weaknesses-short shelf life and poor resistance to water, alcohol, heat, and alkalis. It is seldom mentioned for its strengths, which include some attractive characteristics:
SEEN ON: A wide range of 18th- and 19th-century antiques, especially French polish and European pieces.
HISTORY: Shellac was first used in ancient China for varied applications, including as a base for lacquer, as a glue, to pigment cosmetics, and to preserve food. Europeans discovered it when trade routes opened up during Marco Polo’s time. It’s since been used as a base for finishes and varnishes—and to re-create the look of Chinese lacquer.
GOOD FOR: A sealing coat before other finishes (for instance, a coat of shellac serves as a great buffer between an oil stain and an oil finish). It’s also used as the base of many wax or oil finishes and is the main ingredient of French polish.
PROS: Protean product with myriad applications that’s nontoxic and dries quickly, yet is quite forgiving to use. Mixed with color, it provides an easy way to repair and upgrade almost any piece or to execute spot touch-ups.
CONS: Does not provide total protection against water, alcohol, or heat.
Categories of Shellac
Natural shellac resin is orange in color and contains about 5 percent wax. You can buy shellac with its color intact or bleached out, with its wax included or removed, and in liquid or solid-flake form.
The orange color is the remainder of a red dye which gave shellac its original value. The dye was separated from the resin and used to color cloth. Orange shellac is a natural toner. It will darken the color of the wood without obscuring it. You can also add your own alcohol-soluble dye to make shellac any color you want. As long as you keep the color weak, you can usually brush the toner on without causing streaks. Otherwise, it's better to spray it on.
The wax reduces the transparency of the shellac on the wood. It also makes the shellac even less water-resistant, and it prevents good bonding when non evaporative finishes (varnish, water-base, and conversion) are applied over shellac. You can buy dewaxed clear shellac (often sold as "blond” shellac), but dewaxed orange shellac is difficult to find in small quantities. You can dewax your own shellac by letting the wax settle, and then pouring or siphoning off the clear part (straining is less effective). If you pour the dewaxed shellac off, do so very gently. The wax is easily stirred up. You can see what you're doing better if you work from a glass jar.
The problem with buying shellac in liquid form is that it is seldom very fresh. Shellac is like milk: It has a shelf life. From the moment the shellac flakes are combined with alcohol, the resin begins losing some of its water resistance and its ability to cure hard. For some time the curing is just slowed. Eventually, the shellac refuses to cure at all. It remains gummy on the wood.
The process is very slow, you couldn't measure it day-to-day, and there's no clear point at which the shellac should no longer be used. Just as with milk, the deterioration is accelerated by higher temperatures. If shellac is kept cool, it may cure hard for a couple of years. (Some manufacturers claim up to three years.) But the curing will definitely take much longer. It's a common rule among finishers never to use shellac that is more than six months old without checking it first.
To check shellac for freshness, put a drop of 2- or 3-pound-cut shellac on the top of the shellac can or another non-porous surface such as glass, and let it cure overnight. If you can push your fingernail into any part of the drop the next day, the shellac is questionable. Wait several more days to make sure the shellac will still cure hard before you use it.
Clear (bleached) shellac has a shorter shelf life than orange shellac. The bleaching that's done to take the color out of the shellac causes it to deteriorate faster. You should be more diligent in checking clear shellac for its ability to cure hard. Unlike orange shellac, bleached shellac deteriorates in flake form as well as in liquid form. You will have difficulty dissolving old bleached shellac flakes, and the solution may not cure hard.
If you find out after you've applied the shellac that it doesn't cure hard, you'll have to remove it with alcohol or paint-and-varnish remover and begin all over again with fresh shellac. You cannot fix a gummy shellac finish by applying a new coat of fresh shellac on top. Though this may give the appearance of correcting the problem, it will lead to greater problems later. The fresh coat will begin cracking much sooner because of the soft coat underneath. One of the oldest painter's rules is, "Never apply a hard finish over a soft one."
One way, and probably the best (IMHO) to ensure maximum freshness, is to dissolve your own shellac from solid shellac flakes. Here's how to do it:
Shellac is very user-friendly. You can brush or spray shellac easily as long as the shellac is not too thick. By adding a drop or two of oil to a rubbing pad, you can apply the shellac to wood by a method called French polishing. French polishing is time-consuming, but it produces excellent results, and it is fun to do. In addition, the common thinner for shellac, denatured alcohol, doesn't smell bad and is not harmful to breathe in moderate amounts.
I hope this was informative for you, to expand your knowledge in wood finishes. Should we continue our discussion covering another finish - Lacquer?
*** All credits to C. Pourny and B. Flexner for knowledge sharing in their wonderful books.
Shellac (/ʃəˈlæk/) is a resin secreted by the female lac bug on trees in the forests of India and Thailand. (The word lac means "one hundred thousand," referring to the number of insects found on a single branch. Approximately 1.5 million bugs must be harvested to make 1 pound of shellac.) The resin is scraped from the twigs and branches of the trees. It's then melted, strained to remove bug parts and other foreign matter, and formed into large thin sheets that are broken up into flakes sheets. Those sheets are processed and sold as dry flakes and dissolved in alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze, and wood finish. Shellac functions as a tough natural primer, sanding sealant, tannin-blocker, odor-blocker, stain, and high-gloss varnish. Shellac was once used in electrical applications as it possesses good insulation qualities and it seals out moisture. Phonograph and 78 rpm gramophone records were made of it until they were replaced by vinyl long-playing records from the 1950s onwards.
It is well known for its weaknesses-short shelf life and poor resistance to water, alcohol, heat, and alkalis. It is seldom mentioned for its strengths, which include some attractive characteristics:
- Shellac is the only finish with a proven track record for longevity. It was the favored finish for quality furniture throughout the nineteenth and early part of the twentieth century. Much of this furniture has survived with its original shellac finish in very good shape.
- Shellac forms an excellent barrier against water vapor (humidity) exchange, silicone contamination, and existing stains caused by water, grease, crayons, or natural wood resins. Many professional refinishers use shellac regularly for their first "sealer" coat because of this quality.
- Shellac is unsurpassed as a touch-up material for repairing rubs, scratches, and gouges in other finishes. It bonds well to almost all finishes without damaging them, and it dries quickly.
- Shellac resin is so safe it is approved by the Food and Drug Administration (FDA) for use as a coating on candy and pills.
- Shellac's solvent, denatured alcohol, is not as polluting to the atmosphere as mineral spirits or lacquer thinner, and it is not harmful to you unless you drink it or breathe excessive amounts of it. (As with most liquids in the shop, you should also protect your eyes.)
SEEN ON: A wide range of 18th- and 19th-century antiques, especially French polish and European pieces.
HISTORY: Shellac was first used in ancient China for varied applications, including as a base for lacquer, as a glue, to pigment cosmetics, and to preserve food. Europeans discovered it when trade routes opened up during Marco Polo’s time. It’s since been used as a base for finishes and varnishes—and to re-create the look of Chinese lacquer.
GOOD FOR: A sealing coat before other finishes (for instance, a coat of shellac serves as a great buffer between an oil stain and an oil finish). It’s also used as the base of many wax or oil finishes and is the main ingredient of French polish.
PROS: Protean product with myriad applications that’s nontoxic and dries quickly, yet is quite forgiving to use. Mixed with color, it provides an easy way to repair and upgrade almost any piece or to execute spot touch-ups.
CONS: Does not provide total protection against water, alcohol, or heat.
Categories of Shellac
Natural shellac resin is orange in color and contains about 5 percent wax. You can buy shellac with its color intact or bleached out, with its wax included or removed, and in liquid or solid-flake form.
Coloring
Shellac is either orange (also called amber, garnet, or button) or bleached (called clear or white). You can use orange shellac to advantage on dark woods to add warmth. Clear shellac is better for light, or bleached, woods when you don't want the finish to add color. See the image of Shellac flakes color below.The orange color is the remainder of a red dye which gave shellac its original value. The dye was separated from the resin and used to color cloth. Orange shellac is a natural toner. It will darken the color of the wood without obscuring it. You can also add your own alcohol-soluble dye to make shellac any color you want. As long as you keep the color weak, you can usually brush the toner on without causing streaks. Otherwise, it's better to spray it on.
Wax in Shellac
Most shellac still contains its natural wax. This wax settles to the bottom of the container. When you stir a can of shellac, you often see the lighter-colored wax rise to the top and become mixed in with the finish. (The wax makes clear shellac appears white, which accounts for the name "white” shellac.)The wax reduces the transparency of the shellac on the wood. It also makes the shellac even less water-resistant, and it prevents good bonding when non evaporative finishes (varnish, water-base, and conversion) are applied over shellac. You can buy dewaxed clear shellac (often sold as "blond” shellac), but dewaxed orange shellac is difficult to find in small quantities. You can dewax your own shellac by letting the wax settle, and then pouring or siphoning off the clear part (straining is less effective). If you pour the dewaxed shellac off, do so very gently. The wax is easily stirred up. You can see what you're doing better if you work from a glass jar.
Liquid and Flake Shellac
You can buy shellac as a liquid or as solid flakes that you make into a liquid yourself. Liquid shellac is sold in 3, 4, and 5-pound "cuts." The cut is a measuring term used universally to indicate how many pounds of shellac flakes are dissolved in 1 gallon of alcohol. The higher the cut number, the more concentrated the shellac and the thicker the solution. For example, you are getting twice as much shellac in a quart of 4-pound-cut solution as you are in a quart of 2-pound cut solution. Most of the shellac sold in paint stores is 3-pound cut: 3 pounds of shellac to every gallon of alcohol. You can use the shellac right out of the can, or you can thin it to whatever degree you want. You should use denatured alcohol, sometimes sold as shellac thinner, for thinning.The problem with buying shellac in liquid form is that it is seldom very fresh. Shellac is like milk: It has a shelf life. From the moment the shellac flakes are combined with alcohol, the resin begins losing some of its water resistance and its ability to cure hard. For some time the curing is just slowed. Eventually, the shellac refuses to cure at all. It remains gummy on the wood.
The process is very slow, you couldn't measure it day-to-day, and there's no clear point at which the shellac should no longer be used. Just as with milk, the deterioration is accelerated by higher temperatures. If shellac is kept cool, it may cure hard for a couple of years. (Some manufacturers claim up to three years.) But the curing will definitely take much longer. It's a common rule among finishers never to use shellac that is more than six months old without checking it first.
To check shellac for freshness, put a drop of 2- or 3-pound-cut shellac on the top of the shellac can or another non-porous surface such as glass, and let it cure overnight. If you can push your fingernail into any part of the drop the next day, the shellac is questionable. Wait several more days to make sure the shellac will still cure hard before you use it.
Clear (bleached) shellac has a shorter shelf life than orange shellac. The bleaching that's done to take the color out of the shellac causes it to deteriorate faster. You should be more diligent in checking clear shellac for its ability to cure hard. Unlike orange shellac, bleached shellac deteriorates in flake form as well as in liquid form. You will have difficulty dissolving old bleached shellac flakes, and the solution may not cure hard.
If you find out after you've applied the shellac that it doesn't cure hard, you'll have to remove it with alcohol or paint-and-varnish remover and begin all over again with fresh shellac. You cannot fix a gummy shellac finish by applying a new coat of fresh shellac on top. Though this may give the appearance of correcting the problem, it will lead to greater problems later. The fresh coat will begin cracking much sooner because of the soft coat underneath. One of the oldest painter's rules is, "Never apply a hard finish over a soft one."
One way, and probably the best (IMHO) to ensure maximum freshness, is to dissolve your own shellac from solid shellac flakes. Here's how to do it:
- Using a non-metal container, combine the correct proportions of shellac flakes and alcohol for the pound cut you want. Suggest you begin by making a 2-pound cut, adding I pint of denatured alcohol to a quart jar containing 1/4 pound of shellac flakes. This will give you the feel of how to do it. You can then try thicker solutions.
- Stir the mixture several times during the next couple of hours to keep the flakes from solidifying into a lump at the bottom of the jar.
- Keep the jar covered when you're not stirring the shellac so moisture from the air isn't absorbed by the alcohol.
- When the flakes are totally in solution, strain the shellac through a paint strainer or loose-weave cheesecloth into another quart jar. This will remove impurities.
- Write the current date on the jar so that later you will know when you mixed the shellac.
- If you want to dewax the shellac, let the wax settle (this could take weeks). Then pour or siphon off the dewaxed layer into another jar. If you're in a hurry, you can try straining the shellac several times through tightly woven cloth until the solution is clear.
Shellac is very user-friendly. You can brush or spray shellac easily as long as the shellac is not too thick. By adding a drop or two of oil to a rubbing pad, you can apply the shellac to wood by a method called French polishing. French polishing is time-consuming, but it produces excellent results, and it is fun to do. In addition, the common thinner for shellac, denatured alcohol, doesn't smell bad and is not harmful to breathe in moderate amounts.
I hope this was informative for you, to expand your knowledge in wood finishes. Should we continue our discussion covering another finish - Lacquer?
*** All credits to C. Pourny and B. Flexner for knowledge sharing in their wonderful books.