It's a friend to all!
Good Old Shellac
© Frank Ford, 8/6/98
Yep, it's the only wood finish that's approved by the FDA as food. It keeps some candies from sticking in to hand, and is the coating on lots of medicine tablets.
It's the oldest clear wood finish, dating back to the time of the Pharaohs
It is, of course, entirely natural; it is also a bit mysterious.
So, what is this stuff?
It's a secretion from a tiny insect that infests trees in India. Known as "lac" (derived from the local word for 100,000) the bugs congregate, live and die on the branches of trees in vast numbers, frequently causing the death of the trees. The resin they secrete is called "shellac" because it forms in sheets (sheet + lac) as it's collected.
Local folks cut off a tree branch and hold it over a fire until the resin melts and drips off. In this primitive form the shellac resin is usually called "seed lac" and it contains a bunch of impurities, including bits of the tree. It's dark brown and about as transparent as gravy.
The shellac is refined in stages and becomes lighter in color and more transparent. Brown seed lac is first refined into "button lac," so called because it is poured out into disks for easy handling.
As the shellac is further refined it becomes the familiar "orange shellac" and "white shellac" (clear, blond, or bleached.) Most finishers these days use orange shellac and clear shellac. Some antiquarians insist on button lac or seed lac for authenticity and color.
The natural shellac contains around five percent wax which is removed in the process of refining and bleaching the clear shellac. The wax doesn't get in the way of most uses for shellac, but stringed instrument finishers generally insist on removing the wax before using it so they can get the highest degree of clarity in their finishes. Most clear shellac is also labeled "dewaxed," which I suppose distinguishes it from the slightly cloudy white shellac you see in paint stores.
In the most ancient times shellac was presumably spread on the surface by heating and smoothing with a hot spatula. In its solid state it has the consistency of sealing wax, and is very brittle. Applying shellac this way is a monument of tedium! Today we only melt tiny globs of shellac onto the surface as a touchup technique, called "burning-in" to fill small divots in a finished surface. Check out my article on stick shellac.
As a wood finish, we use shellac resin dissolved in alcohol (old timers called this liquid shellac "shellac varnish.") In fact, alcohol is the only solvent for shellac, and even then it takes quite a soak for the solid shellac to dissolve. Most alcohols will work, although the lower the boiling point the faster drying the shellac is and the better it works as a finish. Ethanol, methanol and denatured alcohol are the most commonly used, and in my experience, they all work equally well. Methanol dries fast, but is the most poisonous. Ethanol (booze) is difficult or expensive to get in high purity.
Denatured alcohol is really ethanol with a small amount of bad stuff in it so you can't drink it, and it works very well. It is important, though, to get a good grade of denatured alcohol. The cheap grades, often sold as "shellac thinner," have too much water or other impurities to be effective in a fine finishing product. Too much water will make the resulting shellac finish come out cloudy looking, and we don't want that!
As a matter of convention, liquid shellac is described in terms of "pound cut," meaning so many pounds of solid shellac resin dissolved in a gallon of alcohol. One pound cut is my preference for most applications on stringed instruments. Actually, I use a 10% solution by weight, because it's easier for me to calculate in small quantities.
When I mix up orange shellac or button lac, I always pour it into a tall jar and siphon off the clear portion a few days later after the wax has settled to the bottom. That way I have a solution of clarified, nearly transparent orange-brown liquid. The clear shellac is just that; it needs no further treatment.
Store-bought liquid shellac is worthless!
OK, I know that's a bit strong, but aside from household painting chores, I really believe that it is worthless. I don't know any instrument finisher who would even consider using it, although most of us have tried it at one time or another. The stuff just doesn't harden and dry properly. It contains a whole lot of contaminates, including water and sometimes even gasoline! Do yourself a big fat favor and stay away from hardware store liquid shellac! Enough said.
Dry shellac comes from woodworker and luthier sources. Even the finest and bestest shellac is pretty cheap stuff considering how far it goes.
Shellac really doesn't brush well. In fact, it's the worst stuff I every tried to brush on. It gathers and crawls like nobody's business, unless you're brushing a first coat onto bare wood, in which case it soaks right in.
Shellac can be sprayed, but you have to be careful not to try to lay too much on at a time. A thick, wet coat of shellac won't level and will try to run or sag much more quickly than lacquer. Generally this isn't much of a problem because the shellac is being used as a thin sealer or intermediate coat.
It's often just wiped on with rags. In its most sophisticated form, the wiping procedure is known as "French polishing." It's an easy and controlled sealer to use by wiping, and you can simply throw out the rag, so there's no spray rig to clean up.
What's it good for?
Shellac is the friendliest finish in the business. It's the ideal undercoat for any wood finish, including itself. It's the only finish that sticks to all other finishes and can be used as an intermediate or "barrier" coat to separate two "unfriendly" finishes, like varnish and lacquer. It can be used as a top coat over any finish, although it's not so durable as most other finishes so it's seldom used for that purpose.
Shellac is the perfect wood sealer under lacquer. There, I've said it again. Shellac sticks to wood, plastic, glue, and the other items we're likely to encounter in instrument construction, and other finishes stick well to shellac, so it's my first choice every time.
Shellac doesn't wear too well, scratches easily, tends to water spot, is obviously not alcohol resistant, so it's not a first choice for modern instruments. It is the first choice of most restorers of old varnished and shellacked instruments, though.
It doesn't react much to ultraviolet exposure, so it tends not to change color over time. That's a good reason to choose orange shellac as a sealer coat when you're going to want an amber tint to the finish. Orange shellac is the natural choice over dark woods and gives them a rich luster Orange shellac gives a fine look to maple and spruce, too, if used sparingly!
Water is the enemy. Keep your mixed shellac well covered and use high grade alcohol to avoid the water that may cause "blushing." This is really only a problem for French polishing, because sealer coats are so thin, the cloudiness really doesn't show up.
Dry shellac has a relatively short shelf life. After a few years, it starts to lose its solubility in alcohol. You'll know when it's no good because you won't be able to dissolve it well. That's the time to throw out the old and bring in the new.
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