Traditionally the concept of a finish on a guitar is to serve two functions, Protect the wood (first and foremost) and enhance the aesthetics. But what if i told you the thickness and type of finish could have an effect on the sound and playability of your instrument, Would you be more inclined to ask these questions when buying your next Les paul? Would you think twice before buying a polyester finished fender,
I remember watching a Video on youtube entitled "PRS factory tour by Shawn Nuthall". Shawn was Showing his collective guests the various finishing Techniques. Shawn made a disturbing point to call this an exorcised Process. According to Shawn, before the finish goes on the guitars, they have such a lovely sound. The Finish itself (Although minor) makes them sound stifled in comparison.
This is quite a long and ongoing debate. In the 1950s and early ’60s, makers like Fender, Gibson, Gretsch, and Rickenbacker used nitrocellulose lacquer (“nitro,” or “lacquer”). Period. Nitro finishes, however, were hard, porous, and somewhat brittle, and therefore aged unevenly and wore relatively poorly. The spraying of these compounds also released a lot of harmful vapors into the atmosphere. Several companies, Fender among them, hit upon “thick skinned” polyester finishes in the late ’60s, which were much more durable and less hazardous to apply. Later still, many makers began using polyurethane, which had some of the look of nitro, but was easier to apply and wore better.
The oft-quoted benefit of nitrocellulose lacquer is that it breathes, and therefore lets the wood of the guitar resonate freely. Which is to say, nitro doesn’t sound good in and of itself, but allegedly constrains the natural tone of the guitar less than some other finishes might. The fact that nitro ages and thins with time, and therefore replicates the look of guitars made in the ’50s and ’60s has made it de rigueur for vintage-reissues, retro models, and accurate reproductions—but its supposed tonal benefits have also made it a must-spray for plenty of contemporary makers, regardless of styling and application difficulties.
A lot of the bias against poly finishes comes from the fact that thick polyester finishes are evident on many budget makes, with the notion that the finish itself noticeably constrains the wood’s resonance. The polyurethane used by many top makers today, However, is a completely different animal. Several makers of high-end guitars—Nik Huber, Paul Reed Smith, Roger Giffin, and John Suhr among them—use polyurethane on the majority of their guitars, with excellent results both visually and tonally.
So is the truth out their? Possibly, but can we ever truly discern it? Since wood is an organic, imperfect material that differs even when cut from the same tree, while other components such as pickups are nearly as variable, a scientific A/B listening test between nitro and polyurethane is nearly impossible. Maybe it’s best, then, to close on the comments of skilled guitar-builder Scott Lentz, who uses both without prejudice: “It isn’t so much the type of finish used, but the skill with which it is applied, the thinness of the final finish, and, more than anything, the quality of the guitar itself.”