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As shellac produces a crystalline structure on hardening it would follow that the faster it hardens, through the more rapid evaporation of the solvent, the smaller the size of the crystal produced and the greater the potentional hardness of the finish. Rapid hardening produces more nucleation centres in the structure, slow hardening means the large crystals produced grow into each other and a softer more easily deformable structure results.

Logic would therefore suggest that the most rapid evaporating fraction would be the one to use. This would normally be the smaller molecule therefore Methanol should be the solvent of choice.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Ok. One last question......I promise. I will wear gloves, so touching the material is not an issue.

I will be doing this in my workshop in my basement. My shop is a 300 square foot drywalled portion of my basement and has no windows. How do I ventilate the area or is it not possbile and "un-safe"?

P.S. - I have a JDS air cleaner and windows do exist but are outside of my shop. The shop is not air tight. What do you recommend?

Thanks,

Doug Ubele

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Guitars...One's too many...Twenty is not enough.

Use a fan to keep the air moving. but not aroud you and your work. You want to pull the air away from your work not blown on your work. A fan the exausts to the outside is best.

I honestly do not see how the solvent can have much effect on the hardness of the final product i

Tell that to everyone who's used the wrong thinner with lacquer, or the qrong reducer with enamels.

Somehow, the solvent does more than just thin the material and then quietly evaporate....

[QUOTE=Mario]

Somehow, the solvent does more than just thin the material and then quietly evaporate....[/QUOTE]

In some cases that is true, in other cases its not. Certainly its true when considering the drying of enamels since that is not drying at all but a form of oxidation and anything that can interfere with that chemical reaction will affect the final outcome. Other finishes pretty much depend on evaporation. Lacquer and shellac for example. I have used the wrong thinner on lacquer and had to wait for it to evaporate, sometimes for several days, but in the end the finish was hard.

All this, not to quibble, but to make a case for ethanol solvent. A lot of French Polishers recommend it over Methanol and for good reason. Methanol is quite toxic..

I've been chatting with a colleague (she has a PhD in polymer chemistry) about this question.

Firstly, shellac is an amorphous resin as opposed to having a crystalline structure. So it's cross linking that's occurring rather than crystals growing.

Secondly, we both agree with John; we don't think it's the solvent that is causing the difference. Though, we do not dispute that there is a difference. We think that the difference is probably due to the relative purities of the solvents rather than the solvents themselves. I won't go into all the technical details, but suffice it to say that for cross linking to occur, there must be water present to hydrolyze the lac. The cross linking reaction produces water as a product, which then goes on to hydrolyze other molecules etc etc. We suggest that there must be an ideal, or optimum amount of water present in order to maximize cross linking, which will in turn result in a harder finish. The methanol probably just has a water content closer to the ideal, than does ethanol.

Now before anybody jumps on me for daring to suggest water in French polish is a good thing; we’re talking very very small amounts of water in the ppm range or below. However without chemical analysis it is purely an educated guess based on chemical structure and polymer chemistry. I don’t suggest people try adding water to their 2lb cut.
PaulB38384.0053240741

A little water..... a little Borax.... some shellac flakes...heat the mess to around 150f, and stir 'til ready. Tah-dah! Water based shellac. Yes, it works, yes, it cures hard, fast, and is even less toxic than alky cut shellac.

For those who don't like to get dirty and work out the exact recipe, Target Coatings sells an excellent water based shellac. It's my sealer of choice....

Maybe, for the reasons Paul mentions, it will cross link better/faster. Sure works well... sands to a dry powder in 10 minutes.

And y'all thought this stuff was simple, eh? <bg>

I forgot to mention that I have a furnace and water heater with a pilot light in my basement right outside of my shop. I guess I now have a potential issue with fire or an explosion. The best thing is to wait until I can do this outside. This stinks because I was originally going to spray, but couldn't because it was to cold outside. I'm moving to California where it is warm.

Thanks to all,

Doug Ubele

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Guitars...One's too many...Twenty is not enough.

It's pretty sad that you've managed to ask the same question in enough forums that you ended up spooking yourself of the process.

All told, you will use about 2oz of dissolved shellc, and maybe 1oz of straight alcohol. I cannot imagine an explosive atmosphere from this! Use some commone sense, use reasonable precautions, but don't go paranoid on us. Geeze....

Have you never heard of a fondu? It's where the host has this little pot of hot grease or whatever that y'all cook in with skewers, right? Ever wonder what the fondu fuel is? Methanol. Yuppies everywhere have been doing it for decades, many fires have been started, I'm sure, but if houses blew up and folks went blind, it'd be off the market by now.

Use your common sense, use reasonable precautions, and get to work.

And if you're still scared of the process, call Target Coatings and buy a pint of their water based shellac, as I said. It works as well, and in the same fashion as the old stuff, without the alcohol. You seem to listen to everyone but me.....

Hear, Hear Mario. I doubt if the risks are calculable.

By the way, I had a quick trawl around on my laptop during a very boring meeting with the finance committee at work today, and came up with the following link. This is the site recommended by William Cumpiano as being the best written account of French Polishing. Of course it all might be rubbish but who am I to argue with him, I'm a Geologist he's, well he's Willaim Cumpiano!


French Polishing

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

We have this link in the resourse section. And I agree with Sir William this is one of the simplest yet correctly informitive lessons on French polishing I have read. For the most part this is exactly as I was taught by my grandfather and as he was taught by his father.

Mario, I am listening to everyone. In fact, I mixed a 2 lb cut last night with denatured alcohol that is 90% methanol. Geez, I wonder who does that? I sometimes post things that will evoke passionate responses.......as in your case .

I plan on polishing this weekend even though I don't have adequate ventilation in my basement, so I am still a bit concerned. However, I urethaned a few shed doors last July and I didn't pass out and nothing "blew up", even with the water heater pilot going. I will have some fans going and open up the 2 basement windows.

Thanks to all,

Doug Ubele

P.S. - I found the above mentioned article a few weeks back and it looks good. I learned a lot from it and will use it as a basis for my first french polishing experience.dubell38384.5741435185

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Guitars...One's too many...Twenty is not enough.

Interesting discussion for sure. I use plain old DA from the hardware store and mix my own flakes. The finish is durable enough for me, however if people have found that methanol may give a harder finish, by cracky I'll give it a shot! Can't learn if ya don't try. As far as exposure is concerned you can wear a respirator and gloves if you're worried. I can't possibly imagine an explosion hazard from FP vapors. Interesting point about shellac curing and water, however I think most alcohols have plenty of water in them already. Everclear is 190 proof and I'd bet my bottom dollar that the other ingredient is water (people have to be able to actually drink that stuff you know). Did I cover it all?

This has been something of an amusing thread, though also informative.

For anyone who hasn't gotten their proper fill of paranoia from this thread, there are plenty of things to avidly avoid that would give your health a much better return on its invested time than eschewing the horrors of french polishing. Mercury for one, is often put in your teeth - right close to your brain. Not to mention its found in a number of household items and things we use specifically like hygrometers.

When it comes down to it, french polishing is much safer, cleaner, and more gratifying than most of the alternatives. And the health issues you avoid worrying about miniscule amounts of chemicals listed on your cans of denatured alcohol are easily negated by the fact that you just cleaned your bathtub with comet and had tuna at the local sushi bar after your flu shot.

There is just no escaping some of these things, unless you want to hole yourself up in a bubble. Many other hazards are never even included on labeling...

regards,
Joshua French

jfrench38384.8618634259

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Instagram: @jfrenchluthier
Web: https://www.jfrenchguitars.com/

Amen brother! Now lets kill this horse...