Nitro vs. Poly
A guitar’s finish, despite being the last in the building chain, is never an afterthought. It’s the final step to make a guitar or break it. After all the parts are set in place and measured to exacting specifications it gets completed. We analyze every detail of our instrument to make sure what we want to hear comes out and the finish is no exception. Through the years there have been many different options yet the major players have stayed nitrocellulose lacquer, polyurethane and polyester. Each type of course has their camp of devotees that will swear by one or the other, but in a market of changing needs and changing climate both finish types are striving to be the best, and if done correctly these finishes can rival each other on any guitar.
To get a basic understanding of finishes and how they work we start with Nitrocellulose Lacquer. Nitro has been the mainstay for decades since it was first developed in the 1920s. Nitro blended with paint extremely well, which made it an easy way for early car companies like Ford to start introducing new color options to their stale black and grey lines.
Nitrocellulose is a solvent-based lacquer in which resin (a clear plant based substance, in most cases cotton) is combined with sulfuric and nitric acids in a process called nitration. This is the same process used to create explosives like nitroglycerine and trinitrotoluene, or TNT. This is why nitro can be a very dangerous finish to work with, as it is highly flammable. Once the lacquer is applied the solvents (chemicals that are able to dissolve another substance) dissolve into the air leaving the resin behind to be sanded and buffed to a high gloss. When nitro first came out it was much faster drying than other options, but today poly has taken the crown for faster finish dry time.
If you are strumming on your new guitar with a nitro finish and you smell that heavenly sweet smell, you are whiffing the solvents as the final evaporation process takes place. Cherish it; it won’t last forever. For those of you who haven’t set foot in a nitro booth to experience the aromatic pleasure of highly explosive substances disguised as ice cream topping, I pity you. On the flip side it is exactly these chemicals that make nitro hard on the environment.
Aside from its olfactory appeal and beautiful gloss nitro is also great finish because it cooperates with other material and substances well. I mentioned before that it was very useful to blend with colors on cars, and the same holds true for guitars. Nitro never cures like poly finishes do. If the solvents that evaporated are reintroduced the layers of finish can be combined making it a very easy finish to repair. Along similar lines, it blends well with pore fillers, sealers, sprays, and buffing products. Flexibility is key for an instrument’s resonance and because nitro never completely hardens, it is less rigid and constricting as other finishes.
The same things that make it great make it less durable. It is softer and can be worn away by materials that react with the resin like a solvent does, such as rubbers on a guitar stand. You may have seen guitars with tacky part of the neck or where the arm rests on the body, this is because it reacts to chemicals and oils much more readily than hardened finishes. Many players consider this a badge of honor on their guitar, a sign of the hours devoted to their instrument. The highly scratched and worn relic look that is popular right now is a display of nitrocellulose’s imperfections. Temperature changes lead to checking (small cracks in the finish from the wood underneath contracting and expanding).
Growing old gracefully and showing everyone where it came from, a nitro-finished guitar doesn’t hide. The Volatile Organic Compounds (VOC) that solvent based lacquers give off may eventually make them a thing of the past, as they are hard on the environment and hard on the respiratory systems of those applying the finish.
Very elaborate and expensive ventilation systems must be maintained to comply with Environmental Protection Agency (EPA) and work place safety regulations, if it is even allowed at all. Many guitar manufacturers locate their facilities in states with lenient air quality laws for this exact reason. Combining the high cost of ventilation systems and the health risks of nitrocellulose could be the biggest reason we have seen a push for non-solvent based finishes like polyurethane and polyester.
Though they have been used as far back as the late 1960s on guitars, in the past few decades polyurethane and polyester finishes have become very popular because they have bypassed many of the complications of nitro finishes as well introducing their own assets such as durability and brilliant gloss. The resin is synthetic and it leaves almost zero solvents in its wake as it cures. Low VOC, which the EPA loves. Chains of polymers (linked molecular units that may be natural or synthetic) are activated by catalyzing chemicals, much in the same way solvents are used in nitrocellulose finishes. The finish left behind is completely hardened and cannot be broken down by solvents. I like to think of it like Jell-O. The hot water is the catalyst that breaks down the chemical bonds of the ingredients and reunites them in a new bond that is hardened, all the while not releasing chemical in the process. This is why poly finishes are so durable and resistant to cracks, scratches and overall dulling of its gloss. If you want your guitar to polish up to a new guitar shine for as long as you own it, then a poly finish is probably for you. Unlike an old nitro guitar showing its age, poly guitars are sipping from the fountain of youth.
VOC are on the EPA’s radar and as necessary regulations continue to be instated to protect our environment manufacturers will have to look very hard at polymer based finishes. Since there are no chemicals emitted to cause health or environmental problems, these finishes, though more costly by the pound than nitrocellulose, save manufacturers a lot of overhead. Bypassing the need for extraordinarily expensive ventilation systems only strengthens the case for an already clean and quick drying finish. In a market of mass production guitar overseas and domestically, the ability to cure a finish in a matter of minutes, and send them on their way is a must. Currently major acoustic and electric guitar companies are employing hand held UV lamps to cure polyester finishes in mere seconds. In this situation the UV light is the activating agent to start curing process. Although it takes seconds now, this process took many years of trial and error to develop. In printing this method was used to catalyze a reaction when exposed to UV light, by putting a photoiniator into the resins. This method also allows for a much thinner finish, which brings us back to the ultimate purpose of this dissection, the tone.
A thick finish, regardless of its composition, can stifle Tone. No matter what process it goes through, the one constant that holds true is that the finish must be thin to maintain resonance. Nitro finishes are almost always thinner than a poly finish due the blending of layers and the method used to apply it. Perhaps this is why purists and tone junkies love them. The fact of the matter is, the more layers you put on the more you stifle the tone, especially in acoustics, where the voice of the guitar is all in the wood. Many guitars have amazingly thick poly finishes that leave a solid body with very little acoustic resonance, which absolutely translates when plugged in. This is the reputation that poly finishes have. You never get a second chance to make a first impression, but luckily for poly finishes new advances that allow for a thinner skin will win players over. Also, do not be fooled by matte finishes. In many cases these finishes are not necessary thinner than their glossy counterparts, but have an additive to render a different sheen level. Poly finishes can be lively and resonant if done correctly just as a circuit board can be dynamic and durable.
Nitro is not an unbreakable chemical bond like polyester and polyurethane. Nitro is not a cocoon, permanent and unmoving, wrapped tightly over your guitar’s body. Nitro is evaporating and leaving your guitar always. You notice this with every check and scratch. You notice this especially on a spruce top guitar where the finish has sunk into the grain lines. The wood under your finish is dead and has been since the day it met its first and last chainsaw. However, it is still moving, expanding, contracting, and vibrating. A finish that gives way under the strength and movement of this wood is displaying its ability to let your guitar ring out and sustain. You will find nitro finishes with this ability and you will find good poly finishes with this ability.
All finishes, whether poly or nitro have some effect on the vibration in the guitar wood and the translation throughout the instrument. While this effect is subtle, it does exist. While this may not be detrimental to the heavily saturated rock guitarist, it certainly could be to jazz or blues player that relies on resonance and dynamics instead of all out distortion and it does have a noticeable effect on acoustic guitars. With the modern techniques of applying poly, the finishes are getting thinner and thinner allowing this resonance to come through more and more. While nitro is still there and going strong in the boutique guitar market, its days are probably numbered in production due to the environmental cost. Which is for you? That is for you to decide. If you like off the wall colors and that are durable and don’t fade, go poly. If you’re more into a classic aesthetic and want your years of playing and road-wear to show, then a nitro finish is the way to go. Either way, don’t to let either one discourage you from getting the instrument you love. If you pick up a guitar and it sounds good, plays well, and has the look you want, go for it. Over-analyzing every detail will drive you mad and remember tone is in the fingers not the finish.
By Guest Contributor: Gavin Wahl-Stephens