: Maybe I'll try it on a sample piece. So is shellac different or the same as
: varnish? If I go to the hardware store and ask for shellac, what are they
: going to sell me?

Warning, Do not continue reading if you are the squeamish sort.

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Shellac is one of the older wood finishes known. It is made from the shells of the Lac beetle, which have been dissolved in alcohol. Basically, when you buy shellac, you get a can of dissolved dead bugs. The name is practically self descriptive: think Shell (bug shells) Lacquer.

Varnish is a plastic resin, which might be a natural resin, like solidified pine sap or pine resin, that is dissolved in a mineral solvent. (naptha, turpentine, etc.)

The big difference between the classification of the two finishes is the type of solvent.

The material can be purified by dissolving the bug shells, allowing sediment to settle, pouring off the clear liquid and letting the solvent evaporate from it. What is left are clear flakes of a natural lacquer which can be redissolved, or heated and applied hot as a thick finish or scratch and dent filler.

The alcohol used can be wood alcohol (methanol) or Grain alcohol (ethanol) or most commonly a combination of the two, which is called denatured alcohol. They add enough of the poisonous methanol to the edible and intoxicating ethanol to poison it and keep people from drinking it. In so doing they also avoid the heavy taxes that are imposed on ethanol.

You can get two basic types of shellac: Orange and clear (or white) and it comes in various strengths depending on how much of it is solids and how much is solvents. These are usually refered to by the number of pounds of solids in a gallon batch. Typically you might see a 3 pound cut and a 4 pound cut. The 3 pound cut would have 3 pounds of solids and the 4 pound cut would have 4 pounds of solids, or be 33% thicker. Dyes can be added to these to change the colors, too.

The material hardens by the evaporation of the solvent. Because of the strong affinity that alocohol has for water, this material absorbs moisture from the air, yielding a somewhat cloudy finish, so it should be used on dry days. Old shellac can absorb enough atmospheric moisture to render it useless. Even unopened cans that are old can turn bad. Get fresh stuff. Use very thin coats and apply a lot of them if you want to build up a finish.

Shellac is frequently used as a sealer. Or, to put it the other way, there are a lot of sealers being sold that are simply shellac. If you can't find shellac at your local paint store, you can probably find BIN sealer.

The $64 dollar question is whether using shellac seals the wood so well that epoxy resin can not later penetrate the pores of the wood. I believe it might, but that even if it does this should not affect the bond between the resin and the wood. It just might be a good thing for reducing outgassing and the appearance of tiny airbubbles. That is just my gut feeling, though.

If anyone in the materials testing field can do a few tests to see how deeply resin soaks into untreated wood, and also into shellac-treated wood, then we might get a legitimate answer. Maybe we could jsut get a thin slice and look at it under a microscope. It would also be nice to see if there were any significant differences in the strength of the bond between epoxy-and-fiberglass-cloth and the two wood samples.

After I wrote this I found a really good website that deals with shellac, and doesn't seriously contradict me -- jsut kinda offers minor corrections

try: www.shellac.net

Hope this helps

PGJ