Guitar Finishes: Nitrocellulose

Let's chat a little bit about guitar finishes. And, where better to start than with the one that sometimes causes the most fuss: Say hello to nitrocellulose.

The history of nitrocellulose is fascinating so indulge me a little on this. In the early to mid nineteenth century, a number of chemists developed mostly the same material at around the same time. My favourite origin story is that of a German-Swiss chemist who accidentally spilled a nitric and sulphuric acid mix and grabbed his cotton apron—the first thing to hand—to mop it up. As he left the apron near the stove to dry, it ignited with a massive flash.

Turns out, this stuff can be a bit dangerous.

Cellulose is an organic compound found in, among other things, plants. Stir it up with a couple of different acids and you get nitrocellulose. Given what happened to that exploding apron, you won't be surprised to find out that one of the first uses of nitrocellulose was as guncotton (the 'cotton' part of the guncotton name was partly because the cellulose used for manufacture came from cotton and partly because nitrocellulose still resembled that fluffy cotton). Guncotton was much more powerful than black powder and was used as a blasting explosive, as well as in shells, mines, and other stuff that's generally dangerous to health. During World War I, British soldiers sometimes improvised grenades by filling ration tins with guncotton and poking a makeshift fuse in the top. Of course, all of these uses assumed that the nitrocellulose hadn't already spontaneously ignited, which it sometimes did.

Fast forward a few years from its discovery and, after various planned and unplanned explosions, nitrocellulose was used with other treatments to make the first plastic (which eventually became celluloid). Among other things, celluloid was widely used to make photographic and cinematic film.

Fast forward another few years and, after various unplanned cinema fires, film stock moved to, relatively less-incendiary, 'Safety Film'. Soon after, a guy called Edmund Flaherty at DuPont realised that he could dissolve nitrocellulose in a solvent (like acetone or naphtha) and throw in some plasticisers to make a substance that could be sprayed to form a finish. And here's where we come in.

Nitrocellulose lacquer

Nitrocellulose lacquer was seized on by the car industry. Henry Ford's crew realised that it was faster to apply, and dried more quickly, than the stuff they had been using. That was enough for Ford, but the fact that it could easily take coloured dyes and pigments meant that they could drop the qualifying part of their "any colour so long as it's black" statement.

Musical instrument makers also cottoned on (sorry) and it was used on all sorts of instruments in the first half of the twentieth century.

Nitrocellulose is an evaporative finish. The solvents flash off quite quickly initially, and subsequent coats can be applied with less delay. Because of these solvents, subsequent coats actually melt into previously applied coats and bond together. It's possible to end up with a thin finish, in easy fashion, from a spray gun. Since you don't want a thick, heavy finish on something like an acoustic guitar top, this is great. As finishers got used to it, they were able to spray a thin finish that could be sanded and buffed to a fantastic gloss.

Pigmented lacquers allowed for great custom guitar colours. Dye allowed for pretty translucent finishes and fantastic sunbursts. It was a golden age for the guitar makers.

Of course, it wasn't all plain-sailing. Nitrocellulose lacquer was still a highly flammable material, dissolved in a highly flammable solvent. This brings plenty of safety issues around storage and usage. When spraying, it's definitely not something you want to breathe, and overspray and vapours remain flammable and harmful. There are significant health and environmental issues here.

Even after it cures, it remains susceptible to many solvents. That means you need to be careful of your nitro-finished guitar. On the plus-side, however, it means repairing those finishes is much more easy. Because the previous coats can still be 'dissolved' newer coats will bond more homogeneously. It's possible to make much more discreet repairs to an instrument finished with nitrocellulose.

As the finish ages, a number of things can happen. First off, it will yellow over time. Secondly, the evaporation of solvents that happened during the initial curing period will continue, albeit at a much slower rate. That can lead to the finish thinning even further over time. This can sometimes be seen as a finish that's relaxed into grain lines in wood. Often, the ongoing evaporation will cause the finish to shrink, leading to many tiny cracks developing. That's the checking we're all familiar with.

The legend of nitrocellulose

Let's think about those properties again. At the time, nitrocellulose was relatively cheap and was relatively fast to dry. It could be coloured with dyes or pigments. It was easy to apply and made the finishing process relatively forgiving. For most people, back in the day, environmental concerns were not terribly concerning, and safety concerns were probably not quite so pressing as they might be today.

So nitrocellulose was used widely. It was the best (read, "cheapest") method to get a good looking finish. It wasn't analysed for its longevity over years and decades. Nobody decided that future generations would probably appreciate some heavy finish checking. Anybody in Fender or Gibson, realising that the finish would eventually turn more yellow and crack extensively, most likely hoped they'd be retired before the guitars started to be returned. 😉

So, if we leave the accidental aesthetics to one side, what about nitrocellulose and its contribution to the guitar's tone? I'm guessing there were teams of world-class musicians performing careful listening tests to determine the best type of finish for tonal acou—

Nah, probably not. See above re: cheaper and easier.

So is it another happy accident that they stumbled on a finish that allows the wood to breathe and resonate in order to impart a glorious tone?

Nah, probably not. Much more likely that the guitars with the tones we've decided are most pleasing happened to be made in a particular way, at a particular time, and nitro just happened to be used as a finish.

Am I saying that nitrocellulose doesn't allow the wood to breathe. Am I saying it has no effect on the guitar's tone? Well, fire up your Indignant Forum Post Input Device because I am.

Mostly.

Does it let wood breathe? I don't know. I'm neither a chemist, an Arboreal Pulmonologist, or a lumber pathologist, but my feeling is that there's not much breathing going on. Does nitrocellulose play a part in the guitar's 'resonance' and tone? Well, the way I see it, a guitar is a system. Everything in that system can potentially play a part in its output. Neck, frets, nut, pickups, bridge, body, etc. What about the screws that hold on the strap-button, though? Sure, they're part of the system but I'm not certain anyone would argue their role is a major factor in the instrument's tone. After a point, the relative contribution of a particular component is probably below the limit of what's discernible when we plug into an amp and listen. I reckon the finish falls below that point.

But, but, but…

Yeah, I know. There are all these guitars with nitro and they sound great. True. But bear in mind that many of them are not 'pure'. Fender starting using Fullerplast (a polyester sealer material) in the early '60s. A decent coat of that will seal the body and fill the grain better than a dozen coats of nitro. And because progress is always progressing, this poly finish was less expensive than nitro, even by then, and faster to apply. As usual, cheap wins over some idea that will be held by players of a future generation.

By the time Fender were offering metallic finishes, they were doing so with acrylic lacquers. Most stuff still got a few top-coats of nitro over the top but it certainly wasn't nitro all the way down on many guitar. Not sure if people consider these instruments as breathing or being resonant.

And the legend?

I'm not sure where the nitro-good-modern-stuff-bad thing came from. I've heard a theory that, when less well-thought-of guitars were being made in the '70s, the thicker, obviously-poly finishes were the easy distinction. It was clear that the finish had changed in some way, so that must be why the guitars weren't as good. In reality, there were a lot of reasons why the guitars weren't good—penny-pinching construction and hardware being high on the list—but the finish was what entered the guitar playing consciousness.

Is nitro debunked, then?

Well, no. Not really. Personally, I don't think the whole breathing-resonant-wood-for-tone argument holds water but I really like nitrocellulose. Accident or not, it looks great. A well applied nitro finish is a joy and the way it ages is wonderful to me. And, being honest, I sort of love the fact that a finish that cracks and checks and discolours over time is seen as a feature rather than a bug.

A splendidly checked nitro finish. Mmm.

From a repairer's point of view, nitro is a much more forgiving finish to repair and touch-up. Completely invisible finish repairs are a more tall order than most people seem to think but you've a much better chance of getting close with a nitrocellulose finish.

Nitro is not without problems and its modern use is more complicated (a chat for another day), but, for most of us in the guitar world, we can still love it. I know I do.

This article written by Gerry Hayes and first published at hazeguitars.com