I decided to make a quick (lol in retrospect) lesson while incubating my article on strings. This particular chapter in The Pursuit Of Tone is a deliberation on the qualities of guitar finishes, which is a slight detour in that it won't be focused purely on tone. This isn't so much an imparting of knowledge as it is a discussion juxtaposed with opinion.
So why is a guitar finished? For two reasons: because it preserves the guitar and because it looks good. I will eventually be discussing the finish's relation to tone (or lack thereof), but first I need to expound upon concepts like humidity and to define the commonly used methods of finishing a guitar as well as their inherent distinguishing properties.
Your Guitar And Its Environment
It is vital that moisture cannot get into or out of a guitar in a short duration of time (anything less than numerous hours). Rapid fluctuations of water by weight in a guitar will absolutely ruin it. The main way the guitar is subjected to these rapid fluctuations is by exposure to less than ideal humidity. Relative humidity of 40-55% is ideal; anything outside of that range is deleterious to most guitars because they will contract and expand, which puts unnecessary pressure on the woodwork. Low humidity will extract moisture from the guitar's wood (causing it to shrink) and high humidity will introduce moisture to the guitar's wood (causing it to swell). Slightly high humidity will cause fret growth and a lethargic tone. Extremely high humidity will even begin to melt the glue joints which hold guitars together. That's how luthiers remove glue-in necks for a neck replacement - they treat the joint with pressurized steam. Low humidity can cause a guitar to do things like go out of tune and fret out. Go extremely low and you can get catastrophic results.
Relative humidity is temperature dependent, so it is also vital to remember that 65-75 F is the ideal temperature range for guitars at a good humidity. Anything too far outside of that range will cause the guitar to warp. High temperature causes expansion and low temperature causes contraction. Coupled with undesirable humidities, this can really wreak havoc on a guitar. The takeaway concept here is that guitars can and do bust right open at extreme humidities and temperatures, so they need to be kept in a forgiving atmosphere.
Despite this, guitars are quite hardy in that they acclimate very well, and luthiers are aware of how to enhance a guitar's resilience to the elements by taking advantage of this acclimation. On the other hand, if guitar makers don't heed this when constructing a guitar, it can lead to very bad things. In regards to acclimation, guitars can survive tumultuous temperature and humidity changes if they are given the time to acclimate. Water vapor takes some time to permeate your guitar, so it will adjust to the new temperature or humidity over time and come out the other side unharmed. The trick is ensuring that the change is gradual. The best way to do this is to keep a guitar in its case. If you bring a guitar straight into a supremely air-conditioned venue before a gig (AC'd in order to compensate for the mob of sweaty human bodies about to assault the venue) from a hot, sunny, and humid day, it's going to play very strangely. It will feel tight and sound unhappy. But if you bring it in its case and let it sit unopened for thirty minutes, it will be much more responsive to play. This is because the smaller a volume of air is, the easier it is to maintain conditions in that space, and the guitar case is a very small and insulated space which lets the harsher external environment slowly seep in. With that said, not all guitar cases and gig bags are impermeable to the outer elements. Some of them suck, and old vintage cases are also often wooden and must be taken care not to be left in hot or cold.
Acoustic guitars are essentially naked, so they are very, very susceptible to changes in humidity. Their construction also makes them more sensitive to changes, due to their tops bellying or bowing. Bridge trusses are designed to alleviate the severity of this issue (and the ~200 pounds of pressure from the strings pulling on the top) and keep the top straighter, but it's not a panacea. For an acoustic guitar, even hanging it on a wall inside your home during the winter can cause the back to contract while the rest of the guitar does not acclimate, causing breaks in the guitar's construction. Since acoustics are so finicky, you can purchase a hygrometer to measure humidity and you can also procure humidistats (humidifiers or dehumidifiers) to keep the humidity at a level that is comfortable for the guitar. (Just as an aside, in-case humidifiers tend to perform very poorly.) If you have to heat or cool your domicile, chances are very good that a humidistat will also be necessary.
Electric guitars also need to be kept in ideal humidity and temperature conditions, but they are far more resilient to changes in the environment primarily because they are SEALED. With the exception of hollowbodies and natural finishes, electric guitars are sealed to the elements by their finishes. This makes humidity far less of an issue and temperature a bit less of an issue. Electric guitars absolutely do expand, contract, and do all sorts of weird things, but it's in a much more controlled manner because they are essentially wearing an insular coat. This point will become very relevant in a bit when I discuss finish types and tone.
Different kinds of woods and finishes expand and contract at different rates. What is crucial in a guitar's construction is for the finish to have an expansion coefficient that is similar enough to the wood's expansion coefficient so that it can accommodate the guitar's expansion and contraction. The reason you see chips and cracks in used guitars isn't just checking and impact bubbles gone awry. It's also from the guitar expanding or contracting too quickly for the finish to accommodate it, and its seal breaks. If the finish is too thick or if the guitar is exposed to low temperatures, finish cracks will certainly appear.
Methods Of Finishing
Here I'll delineate and describe the commonest methods of finishing guitars as well as the pros and cons of each in terms of longevity and appearance. There are high-gloss finishes, toner applications, sunbursts, and many more details of finishing a guitar which complicate the general process. I won't go into all these details, but instead will just present a compact overview of the different finishing methods. I won't be talking about acoustic guitars and I won't be mentioning water-based lacquers, only solvent-based lacquers.
Finishing is a process which can be applied to any wood in order to seal it from the elements and/or give it an impressive aesthetic. Finishing instruments in particular provides a highly durable finish and brings out the figured depth of the tonewoods. In the case of hand-finishing guitars, the process takes about two weeks in total, and consists of many carefully applied layers that are sanded down after each application to eliminate any structural or cosmetic flaws. The detail of this process is often measured at accuracies around a hundred-thousandth of an inch. Immediately after the final sanding of the guitar woods, the pores and pockets of the wood are filled, then comes color, then several coats of lacquer (anywhere from 2 to 25), in between which the finish is leveled and smoothed. A final round of buffing out the finish results in the glossy reflection we all love. During the buffing, the lacquer is "rubbed out" with increasingly finer sandpaper and then is passed over by pedestal buffers (those machines with rotors which buff the finish to its final, mirror-like shine). It's time-consuming and labor-intensive but it makes a difference in the overall product. Mass-finishes, on the other hand, can take just one day (in the case of catalyzed finishes) and are sprayed on by highly accurate machines. So you should really pay attention to and appreciate the work that goes into hand finishes and how much better they ultimately look and feel. It's worth noting that all large guitar manufacturers use the same finishing materials formulated by the same few companies (e.g. Lawrence-McFadden) and so what the quality really comes down to is the manpower that went into the finish.
In the guitar industry, the term French Polish means a particular French shellac varnish that's been applied by the French Polishing method, which is when shellac is manually applied to wood with a cotton pad. All of the fine classical instruments were French Polished, as are many high-end classical guitars being hand-made today. It is a highly respected finish because it is difficult to apply well and because it enhances the luster, texture, and color of the wood. French shellac is very thin and flexible and possibly allows for the clearest representation of the sound from the vibrating wood of the guitar. This attribute is essential for the soundboard on acoustic guitars. The French Polishing application method uses minimal materials: shellac dissolved in a denatured alcohol solvent, pumice, oil, and a polishing pad. Despite this, achieving a professional quality finish takes an expert finisher and a sh-tload of time. So it's a beautiful finish which requires loads of craftsmanship, but it's only applicable to very fine acoustic instruments (because it is so very easy to damage), so I will move on.
Catalyzed polyurethane is the polar opposite of the finishing spectrum. It hardens, with the use of a catalytic reagent, to an abrasion-resistant lacquer and requires almost no manpower to apply, and for this reason is ubiquitously used by the major companies. It's the easiest and least time-consuming for factory setups to work with but it's also quite toxic. Both polyurethane and polyester are very versatile and can be catalyzed with a hardener so they're quick to apply and very difficult to mar henceforth. Polyester gives a glassy finish due to its high solid content, has excellent filling properties, and doesn't sag or crack easily. Although it is very durable and transparent, it can be undesirable as a finish because it can be quite "plastic-y" and eventually takes on a subtly hazy appearance (due to its affinity for cross-linking, for those of you that know your intermolecular properties of the synthetic polymers) that scratches easily. So it's a great option for the guitar industry, because the manufacturer can apply a polyurethane insulator, a polyester sanding sealer, and a polyurethane topcoat, and the guitar is done and looks great. However, if a guitar is going to really be made lovingly, you'll find that few makers opt for polyurethane finishes.
This finish material has been the predominantly used finish by U.S. Musical instrument factories since the twenties. Most vintage guitars have this stuff, and it has been and continues to be well-regarded. Nitrocellulose is actually nitro combined with other resins dissolved in a lacquer-thinning solvent (think toluene, xylene, acetone, etc.). The features of this volatile solvent base are nitrocellulose's acme and downfall - a double-edged sword. This is because lacquer-thinning solvent is strong enough to dissolve subsequent coatings together, which makes the finishing process a breeze. The lacquer can also be dissolved by its original solvent, so any touch-up or finish repair is easy compared to other finishing systems. The main drawback of solvent-based finishing is the hazardous nature of the evaporating solvent itself; exposure to the solvent vapors is a health risk.
Nitrocellulose is hard and durable, yet flexible, and can easily be buffed to a beautiful high gloss when cured. It's also not too difficult to apply because it can be sprayed on, due to the solvent evaporating and leaving the resin behind on the wood surface. Transparent or opaque colors can even be added to the lacquer for artful appearances. Nitrocellulose yellows with age, which can be desirable over certain woods because it makes it look warmer in color, but it might also look bad if you want bright colors to retain their brilliance. Thin Skin Nitrocellulose does the same thing as any other nitrocellulose finish, but in a patently less protective manner. I wouldn't recommend it because it's a fad product.
I prefer nitrocellulose finishes for the way they look and feel. They have a distinct feel, I promise. They're less... rubbery, especially as they thin over time. They also provide the guitar a sort of brilliant, three-dimensional gloss that I really find to be sexy, and I laud the extra dedication required to produce an outstanding nitrocellulose finish.
Satin finishes are not unique. They use the exact same materials as used in any of the aforementioned finishes, but they are their non-glossed counterparts. Satin finishes simply incorporate chemical additives which cause the finish to dry without the glossy sheen. Satin finishes are less labor-intensive and therefore can be found on less expensive models, but that in no way makes them inferior. Lots of people prefer their look and feel. They are slightly more susceptible to the elements, though. A downside associated with this is that satin lacquers will get shiny spots over time being played where contact has worn them down.
Oil finishes are essentially varnishes because they congeal into a hard film upon exposure to oxygen, much like glue, but not by the evaporation of the solvent like lacquer or shellac. I don't enjoy the squeaky, sticky neck feel from playing a gloss-finished neck with sweaty palms. For playability, I greatly prefer a neck finished with tung oil. I'm jubilant about the guitarist community slowly coming around to this same preference.
A tung oil finish is used for that natural, playable feel, but metes enough protection for the wood not to be warped. The lower the porosity of a wood, the better it takes to an oil finish. It's a very quick, simple application process: after the final sanding, the stain is applied and dried overnight, then saturated with the tung oil and dried. The wood filler is then applied and dried and several coats of tung oil are applied to the desired result. It's a very easy, attractive, and functional finish which really works to maximum potential on a neck because it shows off the natural luster of the wood while still feeling comfortable.
Finish And Tone
The theme of this article is that the guitar finish does not affect the tone of an electric guitar. Now that you understand the purpose and methodology of finishing a guitar, you can put two and two together and see why this is a fact. Companies and other proponents of guitar finishes like to claim that their particular finish allows the guitar to "breathe." They neglect to mention that the guitar has multiple layers of paint and lacquer (and sometimes varnish or a decal) on it that would muffle any sort of extra resonance that could come from a simple stained finish. Plus, if the guitar is sealed well enough that it is not entirely exposed to the elements, then no particular formula or application technology used in the finish is going to make a bit of difference in its tonal profile. It doesn't "breathe." The wood is dead. Promotion of this characteristic as a reason for a finish being superior is null and void. If the guitar is an acoustic, the finish does make a minute difference. But in electric guitars, the amplified tone is a sealed system; what you're hearing from the speaker is not emanating off the instrument acoustically, but is entirely sensed through the pickups, so using a thin finish or a thick finish isn't going to make any difference in the electric tone. I'm willing to bet very good money that if you took an electric guitar with a modern finish, recorded it, stripped it of its finish, and re-recorded it, the two samples would be tonally identical. Let's go back to the two reasons a guitar is finished: for aesthetic appeal and for protection from erosion. That's two reasons, not three. Tone is not a factor. If a guitar's finish is an ample protectant, then it certainly cannot be a benefactor to tone. You should be considering the two reasons I mentioned when considering what finish to opt for; tone should not be in that equation.
Now it's time to briefly discuss care of your guitar's finish. Because it's unwise to introduce moisture into your guitar, you should not put mineral oils or whatever on any part of your guitar that does not have a proper finish. The wood doesn't need moisturizing. The oils do buff your guitar's finish and make it look better, but they are damaging to the actual wood (especially to naked fretboards, where the wood isn't protected). Putting oils on naked tonewood itself is sinful and is purely for aesthetics (except for oiled necks, for playability). Many of the companies that make these oils know this and are being exploitive. The phrase "snake oil" comes to mind. I could explain this further but I don't want to digress into a tangent. The parts of your guitar that are gloss-finished should only have waxes applied. Satin finishes should never have anything applied. Guitar straps (leather ones and especially vinyl ones) do wear off the finish and it's a good idea to see where and how your guitar's strap contacts the body. Is your strap in direct contact and rubbing against the finish when it swivels? Is the finish thin enough that this could be a problem? Also never leave your guitar in direct sunlight and do not put papers in your guitar's case directly contacting the guitar, as this will leave permanent marks on your finish. The last habit that must be adopted in the care of a guitar finish is the regular wiping down of your guitar after play. Most guitarists know that their body leaves residual oils and, sometimes, sweat on the guitar, and that those residues depolymerize the finish; they just don't give a f--k. Not a problem, and even a good idea if you want to relic your axe, and you can rest assured that it will have absolutely no effect on your electric guitar's tone. But if you want to preserve the finish, wiping it down with an ever-so-slightly damp cheesecloth followed by a dry cheesecloth after use is the primary way to do so. Let me know what you guys think about guitar finishes and what you do to maintain your axe's finish.
Aside & Closing
In my first article on the pursuit of tone, I wondered in writing about whether a guitar made of a metal such as aluminum would be harmonically rich because pickups respond to electromagnetism, and the strings are metal. Several companies do make guitars out of metals, and they do sound quite good. However, it turns out that aluminum would only contribute to mechanical resonance, and not be sensed directly by the pickups. This is because the remanence (the measure of strength of magnetic field emanated by a material) is rather low for aluminum, as well as for chrome. There are different types of magnetism, and the strongest type by which guitar strings and pickups communicate with one another is known as ferromagnetism. Ferromagnetism is only present in Iron, Cobalt, and Nickel, and all of their alloys (i.e. steel). A few other rare earth metals like Neodymium exhibit ferromagnetism as well. Other substances (like aluminum) do respond weakly to magnetic fields with two other types of magnetism knows as paramagnetism and diamagnetism, but it's not strong enough to make a guitar made of those materials substantially more harmonically rich than a guitar made of a tonewood. If a guitar company did make a guitar out of cobalt, iron, or nickel alloys, it would be far too heavy to run around on stage with. When I brought up metallic guitars in the first article, I was aware of ferromagnetism but I had forgotten to mention it, and I then had to do some thinking and research to realize what the reality of it would be. I'm sneaking this in now because this topic will resurface in my upcoming article on strings. I hope to see you informed readers stopping by in the next installation of the Pursuit of Tone on the topic of strings, coming to you soon. Until then... Happy tone hunting!
864, 993 people have oily wood.