Spraying versus french polishing

[Jim Bancroft]

Question- I know these are just methods for applying finish, but is the outcome different.
If shellac is sprayed on and buffed out is it going to look different, in any way, versus, if it was applied with a pad, in the french polish method.
I can't see where there would be any difference once the finish was completed, but I'm not an expert on this stuff.

Jim

[Bob Webster]

Hi, ;Jim. First off, there is no finish that is tougher to spray well than shellac. Aside from filling the air with an intoxicating solvent that contains denaturants that are toxic to the liver, shellac will go orange peel on you because of the excessively rapid evaporation of the alcohol. That's big bother number one. Someone who is really good with a gun and is shooting LOTS of coats of very thin shellac at low temperatures might be able to beat the orange peel to some extent, but the surface will definitely need rubbing out and buffing.

That brings us to the second issue. If the shellac is sprayed and rubbed out, it will leave very apparent witness marks. The finish takes on a real bizarre and disturbing look to it.

The rubbing on of very thin layers of shellac using the French polish method gets around all of these problems by achieving an amalgamation of each layer with the next through the prolonged presence of alcohol as you're rubbing the finish. AND, the resulting surface can be rubbed out with 1000grit sandpaper lubricated with olive oil A couple of bodying coats later with 1/2lb cut shellac and the surface can be buffed out with the two finest grades of Menzerna to give a surface that people will swear is nitro. For an excellent tutorial on FP, see the Milburns' offering at http://www.milburnguitars.com/fpbannerframes.html.

Cheers,
Bob

[Jim Bancroft]

Bob,
Thanks for the response.
Actually I have sprayed shellac a number of times with great results, and had none of the problems you mentioned.
I'm using a high quality spray gun in a spray booth with proper ventalation.
I suppose any finish can have toxic effect, but shellac seems much better in that regard than lacquer, maybe I'm wrong.

My question basically is, can a person see a difference between a quality sprayed on shellac finish versus a quality french polished finish.
My take on this is, there should be no difference. Spraying and french polishing are just different techniques for applying the finish.
Thanks
Jim

[Bob Webster]

Actually, the witness mark problem can be a real problem and I'd love to know how you get around it. What is your spray routine like?

Bob

[Jim Bancroft]

Bob,
I guess I don't understand the term,"witness mark", what is it exactly?

I spray 1 lb. cut, numerous thin coats. No problems at all, no orange peel, not any kind of problem.

The last project was a 1926 Martin with some botched up finish. The original finish was shellac, and I suppose it was french polished originally. Anyway, I tried french polishing over the original finish, and not having much experience with french polishing, I was making the guitar look worse. Actually removing finish instead of adding. I set the guitar aside and thought about it for awhile, and decided to try spraying the shellac. Not a problem spraying at all, probably built up 5 to 6 thin coats over the original finish, set it aside to cure, and rubbed it out same as lacquer. The finish turned out beautiful.
So that is why I had the question about the difference between french polishing and spraying.

It appears to that the outcome is what matter, not the method of application. With my experience it is just easier to spray it on than french polish it on.

Jim

[Bob Webster]

Hi, Jim. Witness marks can happen as the consequence of rubbing out a finish. With a multicoat layer of finish, most of us are just not good enough at manual sanding to confine all the scrubbing to one specific coat of finish. The result is a bunch of halos, streaks and other artifacts at boundaries of "rub-throughs". Some finishes are notoriously bad about this and others are more forgiving and it really depends on the chemistry of the finish and the ability of the last coat to amalgamate with the previous one. Synthetic finishes are the worst. Shellac is somewhat forgiving and the witness marks from spraying can sometimes be removed via buffing. Depends on how long the each coat takes to dry. The longer the better.

Bob

[Jim Bancroft]

Hi Bob,
Ok, now I understand witness marks. No, I've never had that problem. I could see that could happen if you are spraying a heaver cut of shellac, but I spray a 1 lb cut and it seem to melt and blend perfect with previous coats. Actually I have sprayed a light mist of just denatured alcohol, just so it would soften the finish to accept the next coat and melt together.
And I always spray thin light coats, waiting a couple hours before applying another coat, sometimes doing fine sanding with 800 grit between coats
I really like spraying shellac and the outcome I have had using it.

Spraying Lacquer is similar, but from what I hear has a lot more health hazards. I've had problems(witness marks) like you mentioned when rubbing that out when I first started spraying it, then I found the "miracle additive" called lacquer retarder. You use that you have no problems with coats blending together.

The shellac flakes I use I purchased from Stew Mac and thin it with denatured alcohol.

Jim

[Bob Webster]

Yeah, when I was shooting lacquer back in the 80s I used to thin the stuff with solvents that had basically a lower boiling point. Retarder, for me, seemed to slow things down more than I wanted. Ah, those were the days.... BTW, my shellac is Behylen's super-blonde in denatured alcohol.

Also, to you and David Houchens, I'd also say that the amount of time between coats is a bit tough to gauge. Too many coats too soon and the finish will crash. Happens with French polish method also. Nothing like polishing through the waist on your third bodying session of the day and seeing everything wipe off of the wood. Jpse Romanillos once said that it's a "heartbreaking method".

Bob

[David Houchens]

Bob, Are you using denatured alcohol or everclear. Everclear cost much more but is only toxic if you drink too much. I would think the alcohol would melt into the previous coat just like lacquer does. I haven't sprayed it yet but I'm going to on my next mandolin. I still like lacquer on my guitars. David

[Bob Webster]

Hi, David. I'm using denatured alcohol. The Oregon builders can get Everclear alot easier than I can and, then, as you say, cost is an issue. My imagination says that sprayed on alcohol would evaporate off so quickly that there might not be as much layer amalgamation as one would get with FP. I suppose I could imagine a wider range of scenarios if I was using Everclear.

As for FP on guitars, I think my choice would be to do anything else on everything but the top, and still French polish the top. This, of course, would be for classicals only. There's still an abiding sentiment among classical buyers that FP has the least effect on how the top processes things. With most buyers, a French polish finish is an expected feature for an upper end instrument. That said, Robert Ruck has made a very prosperous and prolific business for himself and uses a catalyzed varnish for everything. He says he can get a very thin finish on the top that is as not-interfering as FP. And, if the client doesn't believe him, they're welcome to specify FP on the top for a $300 upcharge.

Personally, I'd love to be shooting nitro again but my shop situation just doesn't support that.

Cheers,
Bob

[FRANK]

isn't french polish a lacquer ? as long as you don't burn through wet sanding should have no problems with halos and any marks I have used it for repairs I like mine to dry fast less time for floaties to float on to my instruments retarder just slows down the dry time which may be necessary during cold weather to avoid blushing white and in the summer time for solvent pop in which the top coat skims over on top and drys to fast not letting it vape off in a spraying situation and adding mills or thickness taking in consideration the weather and the mix or cut and humidity .although about halos I have seen this on classical Guitars this is cause finishers 70% of the time put a color or tint in just before the last coat if you break that or burn through and proceed with a top coat yes halo but if you wet sand a few layers off then apply your new coat with a matching color or tint no problem I worked for a chemist and a finish shop for years seen halos and have come up with this great fix don't be afraid to wet sand off some color it is usually on top under the second to the last coat this also gives a better way to remelt into it self

[Frank Ford]

French polishing is usually done with an oil (nut, linseed, olive, etc.) along with the shellac, and the oil becomes part of the finish, so there would be a chemical difference. That said, spraying shellac can be VERY problematic because of surface tension issues that cause it to run and "gather" as it flows together.

[Matt Hayden]

FP with a drying oil like walnut oil (the way Gene Clark teaches) seems tougher than FP without in my limited experience. I've tried spraying it and gave up. FP is easier overall and much easier to repair.