One of the oldest clear finishes known is still among the best finishes for wood. Over in India, a small red insect attaches itself to a tree and secretes a hard coating to protect itself while it sucks the sap from the tree. The female lays her eggs inside this sac to protect the larvae.
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This bug is called the Lac bug. The coating is stripped from the tree and processed into shellac. Shellac is most often sold as dried flakes. It is dissolved in denatured alcohol and applied to surfaces. This has been done for centuries and is still used widely today.
The raw sac, with the twigs cleaned from it is least often used today, but is still available. A little cleaning creates what is called seed lac. When it is processed using heat and solvent, it becomes either button lac (the liquid drips and makes buttons) or it is stretched into thin sheets and broken into the flakes most often used today.
Natural shellac has a wax content of 3-5%. Part of the processing gets rid of most of the wax, making de-waxed shellac with a wax content near zero. Shellac also has some coloring in it. The general term for the natural is orange shellac. This shellac, although drying mostly clear, gives a warm tint to the wood it covers. As the color is removed in processing it progresses through what is called blonde to clear.
Zinsser Bulls Eye Amber Shellac
The subject of this review is not the typical flakes that must be prepared overnight before use and quickly becomes unusable after mixing. This shellac is pre-mixed with added stabilizers that allow Zinsser to promise that it will be usable three years after the manufacturing date on the can. This shellac is called amber, the Zinsser trade name for orange, or natural colored, shellac. It is not de-waxed.
I usually buy just enough for the project at hand since the promise stops when the can is opened. Shellac is mixed or sold in different viscosities (thicknesses). The most often used is what is called a three pound cut. This means simply that you use three pounds of shellac flakes dissolved in each gallon of denatured alcohol. Although Zinsser has other cuts available, this one, and all you will find in retail stores, is a three pound cut.
It has the best trade off of workability and film buildup. If you want to use a lighter (thinner, lower viscosity) cut, you can add more denatured alcohol. Some uses of shellac call for a one pound cut to get good penetration and a thin film.
What is Shellac Good For?
The most often thought of use is to put a protective coating on wood. This can be done by brush, rag, or spray. Brushes are most often used. The applied coat of shellac dries to the touch in 15 to 25 minutes. This reduces the amount of time for dust to settle. It is sandable in around one hour. Several coats can be applied in one session. It is frequently recommended that the first coat be thinned to a 2 pound cut to achieve better penetration into bare wood. Subsequent coats melt the previous coat allowing a very tough film to build.
The look of this amber (orange) shellac adds a slight warming tone to the wood while still letting the natural look of the wood show through. The finish is nearly a gloss but can be easily changed to satin or even flat with a light rubbing with pumice and wax over the last, dried, coat. Light sanding between coats is recommended for the smoothest finish.
Another technique, using shellac with a drying oil, is called "French Polishing". This is considered one of the premier finishes for fine furniture made of the darker woods like cherry or walnut. I don't know how to describe the look of this finish, but once you see it, you will likely never be as satisfied with a lesser technique. It is hard work and I haven't tackled it yet. I will someday, though.
Shellac is one of the least toxic of finishes. A major use of the clearest shellac is in food and medicine coatings. It is obviously safe for wooden table ware.
Shellac is also generally non-reactive in the presence of other finishes. It is often used in a one pound cut to seal wood before a stain is applied or to provide a good bond between oil-based sub-coats of finish and water-based top coats.
A major use of shellac is to stop bleeding of resins from wood knots or pitch pockets. A couple of coats will do the job. I have used it on walls where I was getting bleed-through of something to allow latex paint to be used.
First, it is not resistant to alcohol, since that is its natural solvent. A spilled beer or mixed drink will ruin the finish. The nice thing is that it can easily be cleaned and repaired, unlike urethane finishes. It is a little water resistant, but leaving a sweating glass sitting on the finish will often leave a white ring. Again this can be easily repaired. It is not heat resistant above about 140F so use where hot pans come in contact with it is not recommended.
The wax in this shellac renders it less useful as a sub-coat for many finish applications, but it works well as the protective coat.
If you plan to use shellac a lot as your main clear finish, I recommend getting the flakes and the denatured alcohol and making your own. For the occasional project, Zinsser Bulls Eye Amber Shellac is much simpler, not much more expensive, and really convenient.
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