Many players think of a guitar’s finish purely in regards to aesthetic considerations and not as another factor in its tonal makeup, but the types of finishes commonly applied to electric guitar bodies all alter the wood’s resonance in one way or another, and therefore affect the guitar’s tone. In the extreme—for example, in the case of heavy, air-tight finishes—they can even impede the way the wood performs, and choke off its voice considerably. Players who know their tone put a lot of stock in the type, quality, and condition of the finish on any guitar, and it’s worth learning a little about the variables here that can genuinely affect your instrument’s performance.
Traditional finishes include oil varnish, spirit varnish, and nitrocellulose lacquer, the latter being that used on the vast majority of vintage electric guitars and still the industry standard for “quality” instruments. “Nitro,” as it is usually referred to, or sometimes just “lacquer,” is hard enough to be buffed to a high gloss, but is also flexible enough to vibrate with the wood; it allows the wood to “breathe” in tonal terms. Nitro can also change hue with age (transparent coats generally go from clear to a golden amber, while colors will sometimes simply fade), and is prone to wear from the constant friction of player contact. The visual effects of this aging process appeal to many players, and they have become one of the tell-tale signs of the “vintage” guitar. Many of these players—the ones in the know, at least—also agree that the amber hues and bare forearm patches are a fair trade-off for a more open and resonant instrument.
Since the early 1970s many more affordable guitars (and some quite expensive ones too) have been given heavy polyester or epoxy finishes, often referred to by their detractors as “plastic” or “thick skinned” finishes. These are both cheaper and easier to apply, the finishing process produces less of a hazard from toxic fumes, and the results survive the dings and bumps of minor abuse extremely well too, so they are appealing to the budget-range manufacturer on a number of counts. But the thickness, rigidity and total impermeability of these finishes can really dampen the wood’s vibration, and make a guitar—relative to the same with a nitro finish—sound tight, choked and nasal. With an awareness of this, many manufacturers have more recently used polyurethane finishes, which represent something of a compromise of characteristics. Polyurethane is relatively easy to apply and more durable than nitrocellulose, but doesn’t seal the wood quite as hermetically as polyester, and therefore encourages resonance a bit more.
These are fine points in any all-encompassing consideration of tone, of course, and the sonic contributions of other components in any given guitar’s makeup will very likely jump out at you more than will its finish. But they are fine points that many sharp-eared players have detected down the years, and they are worth noting. Many guitarists have sent beat up old instruments away to be refinished and restored, only to find that they just didn’t sing and resonate in the same way after they returned with their nice, new coats of paint. In some cases, a guitar buyer might find that an instrument with a heavier finish even yields a preferable tone—one with more tightness and cut when heavily distorted, for example—but in most cases it is desirable to allow the wood to resonate and contribute its own natural tonal characteristics to all the other ingredients that come together to make “your tone.”