Shellac flakes slow to dissolve

[Patrick Hanna]

Okay, Bob. So much for my afterthought. I'll see what I can find. Thanks!

[David King]

You can buy 90-91% and even 99% rubbing alcohol but that stuff is nasty smelling. I wouldn't go near it. You might as well cut with acetone at that point.

[Waddy Thomson]

Cutting alcohol with Acetone wouldn't be all that bad. Acetone is not very hazardous. As a matter of fact, the body produces Acetone. Plenty of denaturants would be worse. As a matter of fact plenty of folks add some acetone to the alcohol to get a faster build when using the "Wet Build" method of French polishing.

[David King]

Waddy, as "natural" as acetone is, one should point out that it has the ability to carry other dissolved chemicals through the skin and into the blood stream. Best to wear gloves (not Nitrile), Latex or Butyle rubber are better.

[Alan Carruth]

I've been using the 'azeotropic' alcohol/acetone solvent mix for a while: two parts acetone to one part alcohol. You NEED good ventilation with this! I wear nitril gloves when French polishing to keep the solvent away from my hands, since it does nasty stuff.

You do have enzymes that break down acetone. Eventually... You have enzymes that break down alcohol too, but plenty of people die of alcohol overdose. The poison is in the dose.

Alan Carruth / Luthier

[Waddy Thomson]

I always wear Nitrile gloves and liners when French Polishing, just to keep from absorbing too much alcohol, much less the Acetone. Also keeps from destroying a guitar top, with player length nails.

[Ron Belanger]

Cutting alcohol with Acetone wouldn't be all that bad. Acetone is not very hazardous. As a matter of fact, the body produces Acetone. Plenty of denaturants would be worse. As a matter of fact plenty of folks add some acetone to the alcohol to get a faster build when using the "Wet Build" method of French polishing.

Hey Waddy,
What is the "Wet Build" method. Couldn't find anything on Google.

Thanks

Ron

[Waddy Thomson]

Essentially, it's cutting the shellac mix about 50/50 with Acetone. Using a very wet pad, wiping on in long overlapping strokes. Dries instantly, almost. Do several sessions on each surface, then let sit a couple of hours. Repeat. After building for a day, then letting it sit over night, polish it up normally. Polishes up very fast. The finish is still very thin, though as the build is mostly going up in fumes. I did a very good finish on a guitar, under pressure, to get ready for a show, in just over two days. All of this is after pore filling, of course. On that guitar I used Z-Poxy. Planning on trying the 5 min epoxy on my next. Usually use pumice.

[Alan Carruth]

The azeotropic mix of 2 parts acetone to one of alcohol works really well for pumice filling as well. It dries so much faster, and gets the shrinkage right out of the way, so you can end up more level after an hour or two of filling than you normally would have by waiting for a day or three. 'Heady and Ready'.

[Ron Belanger]

Thanks a lot. Another technique to add to my arsenal.

[Simon Magennis]

I am another with "antique shellac" - I am not sure how old the stuff I use is as my wife bought it. I certainly think we have some that is 15 or more years old. We take no special precautions - the flakes are in the original plastic bag in a cardboard box in a cupboard in my wife's studio. Sometimes it takes a bit longer to dissolved buts thats mainly because I forget to stir it and end up with a big solid chunk in the bottom of the jar after it sitting overnight. If I start the batch in the morning and stir regularly then there is no problem.

[Andy Birko]

Unscientifically speaking - I've noticed that the more processed the shellac, the more susceptible it is to this effect. i.e. dewaxed super blond seems to go bad after a couple of years while garnet or other dark shellacs seem to have a much longer shelf life.

Early in my luthing journey, I discovered that I like dewaxed super blond a lot so I bought like 2 or 3 pounds or some other really big quantity and I found that after a few years, it had melted into a big lump in the sealed container. I saved the flakes that weren't stuck together and they still dissolved ok but the big mass wouldn't, even when ground up.

I too suspect that this has something to do with moisture.

[Patrick Hanna]

Hello, Friends.
I have been unable to get back to this for a few weeks. Here is an update:

The shellac batch which prompted my inquiry was mixed in mid-October with alcohol that had been opened frequently over a period of about six months. When I left for a one-week vacation on Oct. 25, it was mostly dissolved, with a few gelatinous "floaters" in the jar. At that point, it had been standing on my bench for several days. When I returned from my vacation, those bits were fully dissolved, too. Yesterday, I mixed a fresh batch in the same proportions in a clean olive jar. As with the October batch, I put about 3/4" of dewaxed flakes in the jar. As before, I broke these into pieces roughly 1/2" square or smaller. I opened a fresh can of denatured alcohol (same brand) for the first time, and added enough to cover the flakes plus about 3/4" of alcohol above the flakes. I gently agitated the jar every 15 or 30 minutes for a few hours. Then once an hour or so. After six hours (still seems a little long to me) only a few gelatinous pieces were undissolved. I went to bed, and those were fully dissolved by morning--much quicker than the October batch. I strained the October batch through a coffee filter, but have not yet strained yesterday's batch. Late this morning I placed two drops of each batch on the bottom of a clean glass jar. I used a clean bamboo skewer to apply the drops and I wiped the skewer clean between applications. I didn't check on my experiment for a couple of hours. Minutes ago, I found both puddles of shellac to be completely dry. Both had leveled and spread a bit, forming slightly raised rings around the edges. These rings were dry, too, and I did not leave a fingerprint in either.

My observation is that the age of the alcohol definitely makes a difference in the period of time required for the final gelatinous bits to dissolve. Six hours of dissolve time still seems a bit slow to me, but I can't remember how fast the flakes dissolved in batches made last year year or the year before. The flakes are dry in their original can. No sticking, no gumminess. Ergo, I presume that they are okay as long as they will go into solution.

Does my test seem about right to you more experienced folks? Do any of you have further insights based on my results?

Many thanks to all,
Patrick

[David King]

Patrick
Good to know, a little moisture in the alcohol makes all the difference.