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Hello,

I just finished up my first uke that is French polished. I followed Tom Bills course (thanks again for the recommendation) and it turned out pretty well. I learned a ton and believe I will improve with the next one. I have a question about French Polish and tone....

My understanding of French Polish as a choice of finish is preferred by many builders for a host of reasons:
- Easy to apply. I can do it on the couch watching TV. No harmful chemicals (if you use grain alcohol).
- Easy to repair. Perhaps the easiest of all finishes to repair.
- Can be applied micro thin.
- Looks great
- Tradition
-Etc....

Much of the material I've read about FP and instruments is that the ability to put such a thin finish is advantageous for tone. This makes sense to me. We spend a ton of time getting the soundboard at just the right thickness, brace it, voice it, then put a layer on top to finish. It stands to reason that we would want that layer to interfere as little as possible with the voice of the instrument.

I've read a few posts here and elsewhere indicating some folks FP only the soundboard. The body, and perhaps the neck, are sprayed with whatever finish the builder likes to use. I like this idea because I had a heck of a time keeping scratches out of the back of this uke i was working on. I also wonder about user expectations. Would potential buyers be so used to hard finishes like nitro that they will be troubled by the inevitable wear that FP would see from regular use?

Adding another wrinkle, I'm working my way through the Gore / Gillet book so I'm hyper focused on what the back and sides are doing as part of the build process.

Question:

Would doing FP top and sprayed B&S really impact the tone? I guess this depends on how thick the finish is sprayed on, but has anyone experienced comparing the two scenarios? Meaning, an instrument that is fully FP compared to just FP the top?

Brad

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"Would doing FP top and sprayed B&S really impact the tone?"

My guess is it would mostly affect the psychoacoustics .

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I would say that the effects would be there, but lots less than what you'd hear on the top. But, if you're spraying, perhaps you can do nitro, which Gore feels is an equivalent to shellac?

But the effects would still be there.

If your instruments are not dramatically sensitive to the type of finish that goes on, perhaps they're not quite as responsive as they can be. In my own guitars, the choice of finish is a profound, indisputable, obvious tonal/response difference to anybody layman or professional. Black and white, no subtly whatsoever. Can I hammer that nail home any harder? The difference is largely in the treble spectrum. And it is not psycho acoustic, I assure you.

I build two brands, one satin, one gloss. The finish on the satin winds up so thin it can't really be measured. The treble response in these guitars is really nice. So light, responsive, airy etc., blah blah.

The last run of gloss guitars I did some experimentation. I sent one to the US and had it done with conversion varnish. I ran out of time for a deadline on two others and had them done in UV poly. The overall volume output and timbral differences was telling. The only difference between the three guitars, woodworking wise, was the finish. All the same voicing techniques, different finish. And yes, different woods, but I'm well versed in the overall sound of my guitars regardless of wood choices and can distinguish the timbral differences that woods make vs the finish. So obvious when they're side by side.

The only caveat I have to go with that is that the CV came home with with a silky .003 gloss, whereas the UV poly came in at .007, which is too much finish no matter what type. So a plausible case could possibly be made saying that it was the amount of finish, rather than the type, that made so much difference. But, when you have a guy as knowledgeable as Trevor Gore saying stay away from all polyesters, I'm going to say the material has a lot to do with it.

If I could find someone that could guarantee absolutely they could give me a .003 UV poly finish, I might give it one last chance, but I think it unlikely to find anyone. Sadly, the man who could do the CV has retired, otherwise I'd be pretty happy with that. But still keeping options open.

For myself, I'm now willing to pay 1000$ to have my gloss guitars FP'd in Royal Lac, a full 1/3 of my base price, until I can learn to do it myself. There is a guy in my berg that does it and I am sure I can pester him enough to show me just to get me to go away, lol.

Oh look, I ranted again. I think I might be getting Heshitis:)

Anyway, back to op...

If you are into the G/G books and use that data to get your instruments into the sensitivity range that they can be made into, you will almost certainly be able to hear the difference, depending on what finish you spray the back and sides with. However, as it says right in the book, Trevor feels that shellac and nitro if applied properly are basically equivalent, then if you're already doing nitro it should basically be a wash. I guess I should have led with that, lol!

It should be mentioned that some finishes will add stiffness as well as weight.

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I have to admit I could not discern the difference between finishes but doesn't there HAVE to be some effect between finishes and thickness as well? What effect that is I imagine could be good, could bad, depending on your definition of good and bad. Is it unreasonable to assume that bare wood would sound better without a finish - but not always. And the converse, is it unreasonable to think that a finish on a sound board could improve the sound - but not always?

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Thanks, Ed. Your scenario with the different finishes is exactly what I was after. Appreciate the feedback!

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Ed, I am an amateur, I don't/can't spray (nitro in the garage = marital issues) .. I FP with regular Shellac and FP with Royal Lac.. I also have padded and buffed Royal Lac.. I like it.. It is a bit tougher to FP than regular shellac but I know several people who do it.. Interesting that there is someone else here in the Vancouver area who is doing it.... Every time I've mentioned Royal Lac to a local Luthier here I've got a confused look in response.. VJ the creator is also very open about answering questions.

To the point of the Original question, everything effects tone.. the question is can you hear it I think it is not uncommon to FP a top and spray the back & sides of a classical guitar

Kerry

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Yes, do not spray nitro, or anything really, without all proper safety stuff. You don't need to kill yourself for this pursuit.

How has spraying the royal lac turned out for you? I have heard of problems with this method. I don't think I'll even try, just cause I don't have a proper safe spray set up...

It's a pretty common practice in classical guitar building to FP the top and Nitro or what ever else the rest of the guitar. I think FP is the best finish on the neck too, it just feels friction free.

"Trevor feels that shellac and nitro if applied properly are basically equivalent, then if you're already doing nitro it should basically be a wash. I guess I should have led with that, lol!"

I don't think you would "hear" a difference between a guitar that was totally french polished, over one that had a french polished top and a properly applied thin lacquer finish. The top being the primary sound generator I think will have the greatest impact on the sound of the instrument. The back and sides do color the sound, but again, with a properly applied thin finish, the change of the color I think would fall in the psychoacoustic range.

On the other hand if you are going to dip your guitars in conversion varnish or poly including the soundboard - a nice thick glossy coat I think you will notice a difference.

I'm trying a wax finish on one of the instruments I am building. As an amateur I can indulge my curiosity. I put a barrier coat of shellac under it, so if I hate it I can clean it off with naphtha and do a F.P or lacquer instead.

Ed

if you are asking me, I have not sprayed Royal Lac for the same reasons as you have not.. I tried it on test pieces with a crappy set up and got crappy results, go figure

I've applied it with a french polish technique and got good results although i find it harder to FP than regular shellac (maybe because of higher solids??) I have also just padded it on in what i guess you would say is a lazy FP technique then let it cure and buffed by hand with first Micromesh then Colortone Polishing compounds... (I see they are on close out at StewMac).. and that worked well.. doing a Weissenborn right now and that is what i will probably do on it.. I do think I will eventually get a good HVLP spray rig and try spraying it again as i have been told it should work..

Kerry

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Thanks. I think I'm gonna just lay out some dough and take a class...

Where do they offer a class around here?

Kerry

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I know a guy that knows how...