Nitro lacquer wins the durability contest, but for nylon string instruments a thin coat of shellac on the top is considered the best for tone quality. I think that is because shellac cures up harder than lacquer,and has lower sound damping properties.
So, French polish already! I do, but in areas adjacent to the bridge and fingerboard that technique "leaves something to be desired". Maybe even "a lot to be desired".
So, I'm thinking once again of spraying shellac, perhaps with an air brush. Anyone have words of wisdom to offer?
I've sprayed a couple of nylon string instruments with Shellac. I can't say I've figured it out. I would love to make it work. One thing I know for certain is the coats must be spaced way out as compared to lacquer or french polishing. A sprayed film of shellac can take an epic amount of time to cure. The Alcohol just doesn't seem to migrate out at nearly the rate of lacquer solvents . It's paradoxical that the alcohol flashes off initially so quickly when spraying, it's hard to lay it down smoothly. I live in Colorado and it is very dry. My best luck spraying was in the early morning when it is cool or even cold. The low temp seems to slow things down enough to get less orange peel.
Jeff Jewitt of Homestead finishes sells an additive called "shellac wet"to aid in laying down smooth coats. I of thought of giving it a try but I'm not sure how it would alter the finished film. I also would hate to compromise the relatively non-toxic nature of shellac.I'm not sure what it's ingredients are. You rarely seem to get something for nothing in the finish world.
There has been quit a bit of discussion about spraying shellac on the Delcamp classical guitar forum. You might try searching the archives over there.
Do you still poor fill with an alcohol/acetone mix? Somewhere I heard you were the originator of that technique and wonder if you still do it.
I'm surprised to find you asking questions here, I think of you as someone who has all the answers for us!
Thanks for the reply!
"One thing I know for certain is the coats must be spaced way out as compared to lacquer or french polishing."
I'm surprised that there should be any difference, unless spraying lays down a thicker coat of finish. Shellac does have a shelf life during which it gradually takes longer to dry. Received wisdom says that is between 6 months and a year for freshly mixed flakes. I mix small batches---4oz Ever Clear to 2oz flakes for 2lb cut---and toss what's left after 3 months, just to be on the safe side.
I've got some of Jeff Jewitt's "Shellac Wet", but I want to see if it has any significant effects on the acoustic properties of the shellac before I use it. Yet another research project! The treble in nylon string guitars is sensitive to the damping qualities of the finish, and I don't want to soften shellac with an additive.
I've tried getting on the DelCamp forum a couple of times, and for some reason haven't had any success.
I thought that I had come up with something new by adding acetone to my shellac mix, but as usual, other people had done it before. It really does speed up the drying of French polish a lot, and I think that it also speeds up the shrinking (curing) of the finish.
And, yes I fill the pores of open pored woods with shellac. I want the pore fill to be clear, or at least translucent. I've tried over a dozen different clear fillers of every sort and description over the last 15 years, and have come all the way back to thin shellac. It's got its disadvantages, but the results are very pleasing, and I can go back and fix it, if there is a spot that isn't properly filled.
One caveat about the acetone thinned shellac. Peter Tsiorba says that it doesn't burn back into an old shellac finish as well as alcohol thinned shellac. He got witness marks. I don't do repairs so I haven't run in to that, but it makes sense---shellac flakes are not soluble in acetone.
"I'm surprised to find you asking questions here, I think of you as someone who has all the answers for us!"
Flattery will get you everywhere with me! The thing that has kept me fascinated with luthierie for almost 30 years is that there is so much to learn. Hardly a day goes by that I don't think of something new to try, or that somebody doesn't suggest a new wrinkle that makes a process work better.
Musical instruments have evolved over a long period of time, and it's a very long term commitment to get to the level where the old timers were.
I consider myself a pretty good journeyman at building a guitar, but making it look pretty, Oy! So I'm open to any and all suggestions on that topic---I'm barely an apprentice there.
Offhand I think the only efficient way to get super neat finish around the bridge is to glue the bridge after finishing the top.
Thanks to modern factory production the bar is considerably higher than it was some decades ago, so even varnish and French polished guitars are supposed to look perfect - without the telltale signs of the luthier's hand.
The violin community finally passed through that period, and now more supports a hand-worked finish that looks a bit too rough for guitarists. Maybe we'll see that change, with the factory produced guitar and its perfect reflective finish starting to appear less handmade, but I doubt we can all wait that long.
You know well my "techno-weenie" approach to building which requires that the bridge go on early in the process---before the soundboard is glued to the sides, as a matter of fact! I guess that classical players are just going to have to put up with a "flaw" if they want one of my guitars.
Having said that, Eric Reid has his French polishing chops so developed that guitars that he has finished look virtually perfect to my eye. Too bad I don't travel anymore, or I would go down to Felton and study with him.:
And, you know my "get it out the door" approach, too, after all these years!
Maybe you could combine approaches and glue the bridge on early with some thin glue and a piece of paper sandwiched in there, so it could be popped off easily before finishing the top.
Or not. . .
Hello again Frank,
"And, you know my "get it out the door" approach, too, after all these years!"
And that's why you can still afford to live in Palo Alto, and I can't (;->)...
You have got me thinking, though. I have experimented with pre-finishing parts, as Loy and I used to do, and it occurs to me that I might finish the top at an early stage, with the bridge and fingerboard areas masked off. The damage that inevitably happens when I scrape down the top binding is fairly easy to fix, and the areas around the bridge and fingerboard could stay nicely finished...hmmm! Food for thought (:->)...
I've tried this and had mixed results too. I used an airbrush and had to thin my regular F.P. cut to get it to spray a "wet" coat. Without the addition of solvent, the shellac tended to lay more of a powdery finish so obviously it was mostly drying in the air before it hit the surface. Adding more solvent helped but the coat was still a bit like sandpaper and the build was very slow. As you might guess, long drying time wasn't an issue for me, it was more like the opposite.
In the end, I used it to apply a seal coat in bare wood repair areas and then used tinted shellac to repair a sunburst on the instrument. It work pretty well for this since thin/light coats was exactly what I needed. To me, an added benefit of using shellac, however it's applied, is that it's easy to reverse any goofs I make. I'm a hobbyist and not as practiced as a lot of the other people posting here. I find that I can't really tell if my tint is going to match a repair until I've applied it and let it dry. Shellac is pretty forgiving when this is an issue.
The result I got spraying shellac for the burst repair still needed to be lightly sanded to get rid of the fine sandpaper finish that resulted but it wasn't much. I did a quick/dirty FP of shellac as a clear/seal coat then wiped on (F.P.?) some lacquer over that as a final finish. It all blended well with the original finish on the guitar after a quick hit of very fine steel wool to "age" the look just a bit.
The guitar turned out looking pretty good once I finished and I'll use the process again for sunburst repairs but I don't think I would try doing a whole guitar by spraying shellac, not the formula I used for FP anyway. I can't say for sure but it seems that I've seen some "off the shelf" shellac finish that may spray better. I can't say how this would compare to a straight alcohol/shellac finish like I use for FP. Ultimately, I had to thin the shellac so much to get a wet coat, the build time became so long and the results were so coarse that, in the end, I think I could FP as fast or faster and probably have a better integrated finish when it was completed .
I've done it with the same siphon feed gun I use for nitro. Nothing especially tricky about it. If I remember correctly I sprayed about a 2# cut. Same pressure I use for nitro.
Why would you want to use an air brush?
Thanks for the reply!
I was thinking of an air brush because they are cheap and would keep my mistakes small (;->)... I'm now thinking that a spray gun is likely a better choice.
I don't know why I didn't get the idea before, but Jeff Jewitt of:
is the obvious guy to ask about spraying shellac. He has written a couple of excellent books on finishing, sells shellac and spray equipment, and was once a guitar maker. He came right back with an answer to my questions about technique and equipment:
Shellac isn’t easy to spray because it dries so fast and doesn’t have a chance to level out. However many people do it. I suggest
Assuming you have a compressor, I’d suggest this little gun here for luthiers:
I used an airbrush because It's the only decent spray rig I have available now. Since I do repairs not new builds I don't really need a larger spray rig. I may get one (again) sometime but it would have more use in furniture/cabinet work than my instrument repair stuff.
I also planned, from the first, to use the airbrush to repair the sunburst, as I have done before. What was different is that I decided to try using tinted shellac instead of straight stain. I found that I like the way it goes on better than the flat look I got with just stain. I thought it was easier for me to see how it was going to turn out as I built up the gradient to blend with the original. I suppose it boils down to personal preference in the end.
Lot's of good info at shellac.net.
I try to clean my gun immediately after using shellac as it tends to gum up.