Official Luthiers Forum!

What is the best oil to use for FP? Olive oil? Does it have to be extra-virgin?
Linseed oil? Motor oil? Ah… What's the "gas out" time you guys allow
between FP sessions, in a stable environment (65?/50% humidity)? How long
do you let the finish cure after the last session and before buffing/polishing?
shellac dries much faster than nitro but I noticed it stays soft for a while. I'm
going to give FP my first shot and re-finish a top that way.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I think shellac dries more slowly, because the solvent is less volatile. It might seem faster since we put it on so thin.

There are a _lot_ of different ways to French polish. Many of us don't use any oil at all until the last coat, and maybe not even then. Oil introduces problems, such as darkening and shrinkage, and the more and the earlier the worse.

Drying oils, such as linseed, and (my favorite) walnut, seem to be at least partly incorporated into the final film. They may actually combine chemically with the shellac resin. The result can be a film that is a little tougher and less soluble in alcohol and (we can dream, right?) sweat.

Non-drying oils, like mineral oil, parafin oil, and olive oil, are not incorporated, and must be 'spirited off' if the film is to dry properly. My early attempts to FP using mineral oil (and, admittedly, less than fresh shellac) were disasters because of this. The shellac was slow to dry anyway because of its age, and the oil just kept it soft for months. Some oils, at least, are attracted to alcohol (I know some oily people like that too, but anyway...) and tend to form a film on the surface which locks in the last bit of solvent.

To remove that film you use (drum roll) alcohol; hence 'spiriting off'. Of course, wiping the sticky surface with a pad that is soaked in alcohol is, let's say, risky. You have to use only a very little solvent, and slowly pick up the oil, which allows the surface to dry a little, and makes the job easier, so long as there's not much alcohol. With luck and skill you can remove all of the oil without the pad sticking.

Some folks cheat, of course, and use something like acetone. No fair!

One could spend a lot of bandwidth on FP. My basic rule is that as soon as it starts to get difficult for any reason, even a little bit, put it down and let is set up for a while. It's a 'Zen' finish: you can only do it by being in touch with what's going on and not fighting it. For that reason it's hard to set down rules about how many 'coats' to put on how often. You just have to learn to do it at it's own pace. The better you are the faster you can work and the better results you'll get, but that's because you learn how to work a little closer to the edge without giving offence, and use a thicker mix.

The other general rule: it's all about surface prep. No matter how good you think your surface is, it's not likely to be good enough. You can't hide anything, or get away with anything, using FP. The finish will let you know when it's ready to be buffed out.

I use very little oil if any but my preference now is walnut oil. What ever oil you use make sure it has no additives. For 'spiriting off' I now use Naptha (sp) which I really like. Easier to use then alcohol and seems to work as well IMHO.

I just got done teaching a two day class today at the local college on French Polishing. I am using many of the techniques I learned from Marshall Brune. With this method I completely French Polished the back of my guitar in a half hour and then buffed it to a high gloss on a wheel the next morning. (you can also do it by hand with the same resuts as a wheel) The sample pieces my students were working on went to the buffing wheel after a 5 minute cure time and had no problems.
The lubricante we use is olive oil but there are only probably two small drops in the whole finish. And then we spirit off like Alan mentioned.

I use Olive oil Extra virgin of means that it has not been mixed with any other oil or additives. So I would say "yes use extra virgin". I would use Walnut but it is hard to come by here in Odessa. I find no issue with having to spirited off. For me the oils is only a lubercant I do not want it as an intrical part of my film. So imo any oil that will not combine with the shellac and 100% rise to the top of the film to spirited off without leave any residue is fine.

Some folks cheat, of course, and use something like acetone. No fair!

Safer, and effective is plain 'ol naphtha. It does nothing to the shellac, yet pulls up all the oils....

My favorite is walnut oil, also. I use it from the get-go.

interesting Mario, and Richard. For me the spiriting process is an intrical part of my leveling process. so I use alcohol, allowing it to melt the shellac a little and flow out high spots when I spirits.

I still consider myself to be pretty much a novice at french polishing, even though I've completed ten guitars to date. I picked up a tip from Brian Burns, using mineral spirits between every few applications of shellac to level the finish. Problem with it is the pad is more prone to stick with it than with shellac applied. I've since found that the occasional drop of (extra virgin) olive oil helps to lubricate things better, reducing the likelihood of the pad sticking. What I usually do after applying fp with olive oil is allow the guitar to sit for an hour or so, then wipe it down with a clean piece of T-shirt material. This seems to work pretty well, really.

I still have not been able to completely fill pores using pumice. Seems like some inevitably gets washed out when I wipe away the excess, using a pad to which I've added alcohol (following the Milburns' approach). So, the pores are softened at least, but still there. It really doesn't bother me, but I've recieved a few comments from players evaluating the instruments about the pores, so I guess I'm gonna have to resort to another pore filling method. I like the simplicity and speed of applying pumice, though.

I've also run into problems with having my purfling pick up some of the color of the back/side wood -- especially cocobolo and EIR. Usually, I'll run an almost dry pad with shellac over the binding/purfling to seal it so that there is no color bleed through with subesuquent applications, but it still seems to happen. My purfling is usually curly maple, and the end grain that occurs every quarter inch or so because of the curl tends to pick up the color more than the rest. I've been thinking that, for my next attemp, I should wipe down the edges of the back and sides and the binding strips with alcohol-soaked swabs prior to installing the binding/purfling to see if this might help some.


Best,

Michael

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Live to Play, Play to Live

For me the spiriting process is an intrical part of my leveling process. so I use alcohol,

Sure enough, that's the tried and true method, but today, we have high grade sandpaper available for that step <bg>

I think one of the big problems many folks have with French polish is forgetting that it was developped before sandpaper and polishing compounds existed. There are no rules that say we can't level it with fine papers and then puff it, or even level it, then rub it again to get the gloss back up, as a cross between old and new.

Shellac buffs to a beautiful gloss once cured. Padding it on VIA french polish seems to compact the shellac and make it hard and tough, more so than if we sprayed it on. after curing a few weeks, it can be handled just like lacquer in the levelling and buffing stages, if we wish.

I use a fine artist's paint burush and paint on a 3# cut of shellac on the pufling, binding, and rosette. I also spray the top with a very light coat of 3#. Allowing it to setup over night. I have had not bleeding issues since I started this. Coco and IRW are bad about bleeding. If you use maple for puf lines. almost any b&s wood will discolor the end grain if you do not seal it well first.MichaelP38663.5613888889

Shellac, like most 'plastics', tends to swell a bit as it absorbs solvent. That's one reason it's hard to get a 'perfect' fill with the pumice method. You get it nice and level and then the stuff in the pores, which is, of course, much thicker than the surface coat, shrinks a lot more. The longer you can wait between fill sessions, and afterward, the better, and it helps to keep your build sessions short, but there's no way to avoid some of this. Personally, it doesn't bother me at all; I like the look of a little wood grain, but the 'industrial standard' finish is 'level as a Lexus', so...

That shrinkage also tells me that 'packing' the shellac with the pad to end up with a denser coating is unlikely. The molecules in the coating have some 'natural' spacing that they will move to as the solvent dries out. As long as there's solvent there, they will be a little further apart than that. The solvent essentially 'stress relieves' the coating, and keeps it from 'packing'. The only way to 'pack' that finish would be do do what they do with 'super balls': melt the stuff, mold it under pressure, and hold the pressure until they've cooled off below the 'glass point'. Can't think of any way to do that on a guitar. I admit this would be a difficult thing to check out. It would be very hard to determine the exact density of that thin coating.

One thing that _could_ happen is that the pressure might align the molecules into 'sheets' on the surface, which might make it a little more resistant to scratching and so on. Again, it's a little hard to think how you'd check that: X-ray diffraction?