Hand Tools Archive
Bill Tindall, E.Tn.
Starting a new thread because the topic emphasis is different.
From the responses below I see that shellac does chemically change upon aging as a result of exposure to oxygen and/or water. This apparent fact kindled more thinking and consulting on the matter. (I eat lunch once a week with some organic chemists and polymer chemists)
What happens to shellac after it gets put on the furniture? Obviously the same as what happens stored in the bag, except faster because it is in a thin layer. So what are the ramifications of this chemistry? Shellac on a 5 year old chest of drawers is clearly not what it was when applied.
Some chemistry. If the molecule is small enough something will dissolve it. Even polymers are soluble in something. The only organic stuff that is insoluble in everything is a cross-linked polymer. At best a cross-linked polymer will form a gel in a solvent that would have dissolved the polymer before cross-linking. With sufficient shear in stirring a gel may disperse and appear to dissolve.
Reactions with water will not polymerize shellac. The reaction with water may form some compound that requires a different solvent mix from ethanol but something will dissolve it.
Looking at the major constituents of shellac there are reactive sites just like in the drying oils (Linseed, Tung, etc) that could react with oxygen. We know that reaction of the drying oils with oxygen "cures" them into tough insoluble films. This chemistry is well understood. The result is a cross-linked polymer.
Hypothesis- The data suggest that shellac undergoes an oxidation that results in a cross-linked polymer. While this result is not good for flake storage, if true, the result would be a tougher more durable film on the furniture after some cure time.
Has anyone ever encountered any discussion of the possibility of shellac "curing" after application?