Official Luthiers Forum!

While searching the net for nitrocellulose info I happened upon a fireworks website!! I have a small fetish for the look and feel for the nitro that was sprayed on old guitars, anywhere from the late 30's to the early 1960's. It's hard to get nitro these days that doesn't have an increasing amount of "plasticizers" in it. I believe this can hurt the tone of the instrument. So maybe somebody that knows more about chemistry can look at this site and tell me if this nitro can be mixed and sprayed. Here's the link:
http://www.skylighter.com/mall/chemicals.asp?Sort=N
-John

Nitrocellulose lacquer, 25% solution - Quart

[C6H7N3O11] Clear to light yellow liquid

A fast-drying, flammable binder and waterproof coating. This is a concentrated 25% solution of nitrocellulose dissolved in 65% acetone and 10% 2-propanol. Use as-is, or for most uses, thin to 5-10% with acetone. 1 quart, screw-top metal can. Shipping weight 3 lbs.


This is a new one on me....

_________________
Reguards,

Ken H

I doubt that this would be a durable guitar finish. Likely it would be brittle and decompose early on by oxidation of the nitrocellulose.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Thanks for the info guys. I wish I could get something like the old ppg farben lacquer.
-John

The 'common name' for nitrocellulose is guncotton. Dissolve it in solvent and you have lacquer. It's probably easier to have someone else do it, though, and those plasticizers are there for a reason.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob, you're right about the plasticizers. It's just that in recent years things have gotten a bit strange, at least with the stuff that the big companies are spraying. A friend of mine refinishes quite a few of the "big name" guitars and he said that post-2006 models (of a certain guitar) are finished in a very rubbery type lacquer. He says those models cannot even be touched up with nitro because it doesn't take. I'm sure there are still some good lacquer brands out there but for somewhat of a fanatic like me, the rapid changes in formula is disconcerting. I own and have had the privilege to play some beautiful old guitars and IMHO, the nitro of that time plays a small but significant part in their sound, and even their look! Like I said I'm kind of a finish fanatic. There are some vintage auto restoration companies around and I think some of them might sell lacquer. I don't know about the quality though.
-John

I'm not sure what the formulas for the old nitro lacquers were, but this material is known to change and deteriorate over time. Are you sure that what you are seeing on those instruments (that you like the look of) is not just the look of nitro lacquer that has aged?

_________________
Rian Gitar og Mandolin

I actually made some nitrocellulose as part of a science fair project on plastics back when dinosaurs ruled the earth. I can just imagine what would happen now if you suggested that to your teacher!

Anyway, there's nitro and there's nitro. Cellulose is a long chain polysaccharide: sugar molecules hooked together is a way that makes them very hard to get loose. By nitrating some of them you can make the whole mass soluble in some fairly nasty solvents. You only have to nitrate about 18% of the cellulose molecules in the chain for the solvents to be able to get a hold and break it up. As the nitration rate goes up the properties change.

One of the original uses for nitro was as a fiber; viscose rayon. When highly nitrated it looked and felt like silk, and it was prized as a material for fancy dresses. One time a young lady at a debutante ball in England had her gown touched by a gentleman's cigar, and she died a couple of days later of massive burns. After that the highly nitrated stuff was banned from consumer products.

Highly nitrated stock is still used for flash paper, and, when fully treated, as a high explosive. As you can see from the chemical formula that Ken H posted (C6H7N3O11) it has fuels (carbon and hydrogen) and oxydizers (nitrogen and oxygen) right in the molecule. All you need to do to 'burn' it is to rearrange things. This goes very fast when things are so close together, and that's what makes nitro a high explosive.

It takes a bit of energy to kick the reaction off, of course. Like all burning, energy is released, and this can be enough to kick over another molecule if it's not dissipated. The low-level nitrated stuff we use as finish won't explode, but it will burn very enthusiatically.

Still, that one molecule in six that is nitrated in the coating is a high explosive; it's unstable, and it only takes a bit of a kick to knock it over, so to speak. This can be supplied by light or heat, and sometimes a molecule will kick over just on a whim. Over time they burn themselves off, and dissapear as CO2, H2O, and NOx. The nitrous molecules react with water in the air to form nitric acid, and that's one of the things that eats at the plating on the metal parts, and causes things to turn orange. And what do you expect the wall to do when you remove one brick out of six, or more?

Compared with things like shellac or varnish, nitro is not inherently a permanent finish. Shellac gets beter with age, nitro gets worse. To think of nitro finish as being in the same league as the varnishes that Strad and his contemporaries used is, as Frank Ford once said, to worship a false god.

I should stop, before I tell you what I _really_ think about nitro.....

Just think of your nice guitar sitting in its case quietly exploding very slowly. Hmm, I wonder if the phrase "quietly exploding very slowly" has ever been uttered before.

100 year old fiddles are very easy to come across and the finish on most of them is still pretty nice. Most of the finishes I've seen on pre-war guitars are pretty funky.

That being said, we still don't have a good replacement for nitro. The water based stuff is too soft and hard to work. Polyesters look pretty good but don't touch up well.

I don't know that any of the varnishes really 'melt' like lacquer, either, though. Polyester does have the 'permanence' that those old finishes had and it can be put on thinner than nitro (though Bob Taylor should have put a giant ad-campaign behind it to dispel the nitro hoodoo as soon as they started using it)

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I occasionally, when spraying nitro over bare wood, get a finish that has what looks to be strings of cotton rising up out of the surface. This may occur in, say a dozen places on a top or back and has a "lint" look to it. This is spraying McFaddens straight out of the can.
This probably sounds like a silly question, but do these "risers" have any relation to the origin of nitro or cotton.
Nelson

That's called "cotton blush," Nelson, and it is caused by the solvents (acetone, alcohol) evaporating before the vehicles (toluene, xylene) do. It's supposed to work the other way around. Yes, you are seeing nitrocellulose fibers. Usually the way to avoid this is to use better quality thinner (the solvents are more expensive than the vehicles, doncha know). You can also add a retarding solvent.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Well whaddayaknow! For once I didn't ask a stupid question!
Sounds like I ought to be adding a little thinner to the nitro, at least for these sealer coats.
I have used, on occasion, Ace Hardware lacquer thinner, but I've been told that one should use thinner from the same manufacturer as the lacquer.
I checked with McFaddens a year or so back and they don't make a thinner.
Any recommendations for "most compatible/most available" thinner for McFaddens?
Thanks, Howard, for heads up on cotton blush.
Nelson

Nitro, and shellac, are 'solvent release' finishes. You dissolve something in the appropriate solvent, paint it on the surface, and the solvent evaporates. What's left is the same stuff you started out with, and it dissolves in the same solvent, so the next coat 'burns in' perfectly.

Varnish is a 'reactive' finish. You thin it out with solvents and paint it on the surface. The solvents evaporate, leaving gummy goo behind. This then takes up whatever it needs from the air to complete the chemical reaction that polymerizes it into a hard film. What's on the surface in the end is not the same as the stuff in the can, and won't dissolve very well, if at all, in the same solvents. With varnish you have to rely on the 'surface energy' of the hardened coating for good adhesion of the next coat, which is why it's a good idea to sand the surface lightly before putting on some more.

This is, of course, a simplified account of things. Some solvent release finishes, such as shellac, go on to react slowly over time, and become less soluble. Epoxies and UV cure finishes don't need to pick up anything from the air to harden, and so on.

Good lord between Klepper and Carruth I shouldn't be answering this...but I've been exposed to a couple of guitar finishers (nitro guys) and to a person they stuck with Acetone. YMMV.

_________________
Eagles may soar, but weasels don't get sucked into jet engines.

Will give acetone a try.

Acetone is a lot safer than most of the other stuff you find in lacquer thinners. Your body produces a little bit of acetone as a by-product of fat metabolism, so you've got enzymes to deal with the stuff. But toluene? Xylene?