Guitar finishes and their properties.

Nitrocellulose vs. Polyurethane

There are several myths flying around about Nitrocellulose lacquer guitar finishes. Many are simply inaccurate, others are outright false. Let me start with the worst ones.

”Nitro is made from wood so it allows the wood to breathe and resonate naturally, improving the tone.”

This statement is generally false. Nitrocellulose is made from cellulose, which is also what all plant cells are made of. However, the manufactures of Nitrocellulose rarely uses cellulose, they much rather use cotton as it’s easier to nitrate. That’s not the worst part of this statement. Saying Nitrocellulose allows wood to “breathe” because it’s manufactured from similar raw material, is about like saying you should be able to breathe under water because it’s 80% oxygen. Nitrocellulose lacquer paints were in fact developed by DuPont in the 1920’s specifically NOT to breathe, but rather to be a sealant against the forces of nature for automotive applications.

I’m not saying Nitrocellulose Lacquer finishes aren’t good, and are good for a guitar’s tone, but they DON’T allow the wood to “breathe”. In fact, the wood in your guitar’s body stopped “breathing” within hours of the tree being cut down; it’s dead now. The part of the tree we use to make guitars, was mainly the water storage and distribution system of the tree, so it NEVER breathed. It moved water up the root system through the trunk and into the leaves where the exchange of all gases actually occurred. It was the leaves that breathed, NEVER the wood.

”Nitro takes weeks or even months to properly cure.”

This statement is utterly false. Nitrocellulose lacquers do not “cure”. Curing is a chemical induced reaction with a set beginning, open time and an end. “Cured” finishes can never be re-dissolved in their original solvents. Nitrocellulose finishes are evaporative finishes, and CAN be re-dissolved in their original solvents. Lacquers dry to the touch relatively quickly, but then it can take weeks or even months to dry completely. This lead to the misconception.

”Nitro will improve the tone of your guitar.”

This statement is misleading. If you were to take that 80’s Polyester finished guitar and spray Nitrocellulose lacquer on top of it, nothing will improve whatsoever. If you were to remove the Poly finish, then spray Nitrocellulose you should hear a “change”. Now is that change an “improvement”? Only your ears can decide that.

What makes Nitro a good finish is that it is very thin, even when sprayed in multiple coats. It does less to get in the way of the natural vibrations of the wood, which imparts a more full tone than a thick Polyester finish. BUT, make no mistake, ANY FINISH that sits on top of the wood, will alter the overall tone of the instrument.

The simple fact is, Nitrocellulose is a good finish, and it’s what was used back in the 50’s and 60’s. From the early 70’s into the early 90’s thick Polyester finishes were the norm, which do sound somewhat “dead” and “lifeless” when compared to older Nitro finishes. This was mainly due to the way these new finishes were applied. See the painters of that time were very familiar with Nitrocellulose and how it was normally applied. So when their bosses told them to change over to this new Poly stuff, they were most often left to their own devises to figure out how to get the same level of quality finish as the old stuff they were used to. Since they were used to spraying 8–12 coats of Nitrocellulose, they simply started there with the new Polys, never fully understanding that the new Polys were all about higher solid builds and less solvent evaporation as compared to Nitro.

As a general rule Nitro has a build of 30% solids, that’s the stuff we see as the shiny finish, and approximately 70% solvents that’s the toxic stuff that evaporates into the air around us. Polys on the other hand are almost the reverse of that, with nearly a 70% solid build and 30% solvents. So you can easily see how the thick finishes associated with the early Polys came about.

The other advantage that the polys had, was that they were very durable and shiny. They were also impervious to the plasticizers in your hand oils, so they were much less sticky feeling to the touch. They didn’t yellow or chip as easily as Nitrocellulose.

Most of today’s better instruments use a very thin Polyurethane finish that sounds much closer to an older Nitro finish than the thick Polyester finishes, while still being very durable and can attain a very high gloss.

What’s bad about Nitrocellulose lacquers is that they are very toxic, and have in fact been outlawed in the automotive industry throughout most, if not all, of the United States for that reason. They are still legal as a furniture finish, and can be bought in many states for that purpose. BUT they have been altered drastically from the original formulas. The Nitro you’re spraying now is not the Nitro of the 1950s because that stuff was banned in 1974 by the EPA.

There was nothing magical about Nitrocellulose finishes.

A thin acrylic lacquer finish will be basically indistinguishable from Nitro, except that it won’t yellow and crack over time. You can add up to 7% Nitro back to acrylic and still get that yellowing/cracking “effect”, which is what Gibson does currently. They pay a monthly fee to do so because of the EPA regulations that state the current maximum allowed Nitro component is only 5%.

Oil finishes such as Linseed or Tung oil will resonate just as much, if not more, because they don’t sit “on top of the wood” like most other finishes. Instead, they penetrate into the wood and mostly fill the grain up to the surface level of the wood. In the end what you see is mostly highly polished wood, not a highly polished plastic coating.

Thin modern Polyurethane finishes do not hinder tone nearly as much as the older Polyester finishes and are much, much more resistant to chipping and scratching than Nitrocellulose.

So all these myths about Nitrocellulose finishes should be re-considered.

Most of it is just Mystery Vibe and Voo-Doo generated by salesmen to sell you an old “vintage” guitar verses a brand new one.

In the end, a 3–4 mm thick finish of Nitro doesn’t sound any better than a 3–4 mm finish of Poly. I can make this statement because I know for fact that most of the factories switched to Poly based finishes years ago and never said a word. This is because ALL OF THEM use this mantra in their shops:

“Manufacturing specifications are subject to change without notice.”

Adapted from original article by Bruce Bennet from Luthier Talks.