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10/12/2010 |
 In the past couple of years, we have done lots and lots of testing and research to figure out why in some cases dewaxed shellac flakes won't dissolve in alcohol. The problem with our testing is so far we haven't found any shellac we can't dissolve in a reasonable amount of time. In the picture above are two bottles of freshly dissolved shellac. We started out with the oldest chunk of shellac flakes we could find, a gnarly block that was too clumpy to sell to customers and was lying open in a hot, humid warehouse for at least two years - more if you include the time before it came here. We broke off chunks and put them in the bottle on the left. In the bottle on the right, we took the same shellac, but pulverized the chunks first into a coarse powder (see picture below). For the first couple of hours we aggressively agitated both samples every half hour or so. In the jar with the pulverized stuff the bits eventually gelled together on the bottom of the jar. We broke up the gelled bit with a handy screwdriver, agitated it some more and went on with our lives. We went home. The next morning, both bottles were dissolved except for a tiny bit on the bottom (in both samples) and a little more agitation took care of that. We used the shellac with no issue for French polishing.
We were therefore very puzzled about the problems Vijay Veiji, the author of an article about shellac in the December 2010 issue of Fine Woodworking, had dissolving his shellac. We were also puzzled about his claim that dewaxed shellac expires after a couple of years and if it dissolves it will take longer to dry. His problem is pretty common but easily solved. As most people have seen, if you spill some scotch on an old French polished table, you will dissolve and damage the finish pretty easily. So age really isn't the main issue. The issue he clearly demonstrates in the article is the importance of agitation. When you have small flakes of shellac and don't agitate, you get the following problem: the flakes start to dissolve, glom together, form a gel and the alcohol cannot penetrate the gel. However agitation and breaking up the gel will solve this problem. Anhydrous alcohol speeds it along. The problem is exacerbated by the hardware store alcohol Mr. Veiji uses - all those molecules of water in the alcohol block the alcohol from contacting the shellac, and result - even after dissolving - in a softer finish. If he used 200 proof anhydrous ethanol he would not have the problem of slower dry times and a softer finish simply because hardware store alcohol has water which gets trapped and leaves a softer finish and other alcohols which have a higher flash point and simply evaporate slower.
 Another thing to mention is that oxidation happens on the surface of the shellac. Bigger flakes, like the ones you get in our Tiger Flakes, have less surface area than lots of small flakes. Also, bigger flakes have more gaps for alcohol. Breaking up shellac exposes fresh surfaces, which is good. When we dissolved our older flakes, we thought that if there really were any substantial amount of shellac that could not dissolve, we would get residue in the container. But we didn't because the actual layer of oxidation is not more than a molecule or three and just disappears.
Now, I will not argue that oxidation of the shellac flakes doesn't take place - just that it happens, is normal, and isn't a big deal. You can avoid the issue using proper agitation; anhydrous alcohol; larger shellac flakes; and storage in a non-permeable container in a cool and dry place. We are now packing our shellac with desiccants that help with the water vapor and pack in a resealable, nylon-impregnated bag which is less permeable than before. By the way, most of the professionals we know who use flake shellac on a regular basis also use mechanical agitation to help lower dissolve times. It's not a requirement but it makes it easier.
In addition to buying your shellac directly from us, you can also buy Tiger flakes from Woodcraft.
Note: In our continuing quest for knowledge and experience, we want to know if you do have any flakes that you cannot dissolve. Please send them to us and let us try to dissolve them. I would love to find a sample that won't dissolve so I have a control for our other testing. |
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