Could someone set me straight? I'm bombarded with confusing info on guitar finishes. Nitrocellulose, waterbased lacquer, oil, polyester... It seems people are using everything. What's best, and why? And exactly what is a polyester finish?
From contributor W:
First of all, there are many different options for finishing guitars. This is for a good reason. Every different coating family represents something unique to its application. Basically, all of the above are used, and more. What final look are you seeking? Each of the different finishes or families gives a completely different look. Most people, when finishing guitars, want the look of glass. The best way to achieve this is by using polyester. A polyester has very high solids (generally 85% plus). It also has very high filling properties as well as great resistance to sagging. But the reason for using it is it gives the look of plastic. The transparency is superior to anything else. Polyester is a sanding sealer, and is used as only part of the overall finish system. The system as it is would consist of a polyurethane insulator (1 coat), a polyester sanding sealer (2 coats), and finally a polyurethane topcoat (1-2 coats).
I much prefer the "natural" look of shellac, but that's because the great old Spanish guitars were finished with it, and I associate it with quality. Having said that, an excellent classic builder, Robert Ruck, uses a modern finish everywhere. I'm not sure which, but one of the finishes mentioned above.
Until a year or so ago I would have said that steel string acoustics could be finished with most anything, but Ervin Somogyi, arguably one of the very best SS builders, now French polishes his soundboards, and says they sound better. He does the backs and sides in nitrocellulose lacquer. So I'm sticking to shellac for the soundboards of my Classics and Flamencos, but still looking for a tougher finish for the backs and sides.
I can't recall the article I read on the scientific testing on Stradivarius violin finish formula. I understood it to be shellac (very high quality from a specific region) and the one ingredient that separated this finish from the rest was the addition of some form of glass, whether silica or similar mineral. Remember that hide glue is so varied in make and preparation that this long forgotten furniture making product could also have been an important ingredient for acoustical reverb. The only drawback of shellac is its lack of wearability, but someone playing classical music isn't jumping into the mosh pit either. This finish didn't come into its own overnight - it took years to harden and be treated with waxes and hand oils, etc. to develop its unique properties. Research on lifestyle, solvent use and trends in this era is the only way to get the information I think you want to know.
Martin guitars have been finished with notrocellulose lacquer and also polyester for quite a few years. Is there anything more beautiful than Keith Richards and Mick Taylor's Gibson Hummingbird acoustic guitars that you hear on "Wild Horses" and "Angie"? They are finished with nitrocellulose lacquer.
No offense, but the place for you to start your inquiries is Bob Flexner's book "Understanding Wood Finishing." By the way, Jeff Jewett, the author and finish supplier and furniture technician and everything else, is a luthier. He's a good one. He is also good at wearing all those other hats (one at a time).
I am not a luthier. I am a wood finisher and furniture technician. I am also the owner of two Les Pauls. My ears are golden (I use Ampeg amps so listen and drool). The guitars have an ordinary nitrocellulose lacquer on them.
I would not fret so much over the finish. The choice of woods is most important and so is the construction/design. Judging by the Martin standards, the finish is there to protect the wood and keep grime from working its way into the grain. Other than that, if you have good woods and good designs, you will get rich and golden tones from your projects.
As a side note, I read somewhere once that they used some unnamed chemical to treat the wood to prevent damage from worm infestations and the chemicals caused a reaction in the wood that changed its tonal quality, resulting in arguably the best sound ever produced by an instrument.
And, I will pick up Bob Flexnor's book. Have read him for years in Woodshop News.
In that I never consider any finish which is not film-forming, I would never recommend oil finishes. Varnish, shellac, lacquer, polyester, 2k urethane, autobody paint, etc is what I recommend. The proof is in the pudding. I mentioned a luthier who is local to me. He uses Dupont autoclears. His guitars fetch thousands and are worth every penny. I have played them and my ears are golden.
I have played the Martin polyester and nitrocellulose lacquer guitars. It is the guitar in hand and all that makes up that guitar which matters, including the finish. But the finish is just a minor consideration.
A good design which takes advantage of the physical properties of the guitar as well as the use of certain materials for the bridge, end nut and even the tuning pegs is unlikely to be killed by one film-forming finish or another. And if you are talking about electric guitars, the differences become even less important. The Ampeg Dan Armstrong is made of acrylic. It sounds great. The Travis Beams were made of some metal alloy and a graphite neck and those guitars were popular for a while. I prefer nitrocellose lacquer because, as one participant said, it is easy to touch up.
As for classical guitars, I have no idea what the accepted sound is. Classical guitarists are note-oriented. They are not intent on getting off on a fading out note listening to its lingering harmonics the way that us Mick Taylor fans are.
Now, just to be cynical, does it really matter? The two more popular guitar players ever, Jimmy Page and Eric Clapton, have and have had access to the most divine vintage instruments. Yet they somehow manage to wreak out of them tones that are no better than Randy Bachman on a bad day. Why? The part of the playing equation you never read in any technical forum is the part that comes from the interaction between the fingertip and the string. That magic is unique to each player and that's a tonal difference that you cannot buy in a store or dial in on your amp.
Anyway, I used an oil based stain on the bare wood. It had been sanded a lot, probably too much, cuz it really wouldn't take the stain (why I say use a darker color and make several applications). Then I brushed on a sandable lacquer sealer. After sanding it looks really nice, and really not shiny (well, if you turn it and look across it, it has a reflection, but no glow yet). Then we used a polyurethane lacquer. I tried to spray it on, but was too stupid to realize I needed to thin it first (it never dried).
Then I screwed up and scraped the area between the two pickups, trying to drill a passage for the leads... doh! That, and the bubinga is so damn hard, I sheared off two strap peg screws in the bottom. It's all done with a crappy Gibson size neck, on a Fender size bridge... but it plays. I think the wood is the most important feature of how a guitar (electric, mind you) will wind up sounding. I suppose if you soak your wood in finish, it could muddy up the sound, but, hey - some people are looking for that. I almost wish I could muddy up mine - it's a bit too bright for me.
Original Fenders from the 1950's which were finished in nitrocellulose were sealed first with fullerplaste, a polyester type wood filler. Funny their original "nitro" finishes are touted as great for tone, given the fact that underneath the lacquer, there's… polyester. You have to seal off the grain with something that doesn't shrink, especially on open grained woods like ash. Polyester is perfect for the task. You can apply nitro lacquer over polyester, but you can not do the reverse.
By the way, lacquer is a very misleading term. The term derives from the lac insect, and indeed, a finish is made from it: shellac. Lacquer doesn't contain any lac whatsoever. Go figure. Nitrocellulose is made from nitrated cotton fibers; it starts out as the main ingredient in smokeless gun powder before it becomes a finish. I digress...
The next finish used on guitars was acrylic lacquer. Acrylic lacquer and nitrocellulose are only compatible one way: You can put acrylic lacquer over nitro, but you can't put nitro over acrylic; it will instantly check, wrinkle, and do all kinds of ugly things. My experience with acrylic lacquer is that it does not have the depth of color or gloss that nitrocellulose lacquer has, it scratches more easily, and is just as sensitive to chemicals and contact with other plastics. I don't believe it was introduced because it was better than nitro, I believe it was developed because it was cheaper, had better color retention in outdoor applications, and was less flammable. Sometimes it's the only sensible choice though, especially when doing custom finish work such as candy apple 3 stage finishes. Nitrocellulose tends to yellow with age. That can be very desirable over wood, lending a warmth of color. But it doesn't look too good on bright colors or metallics you want to retain their brilliance. So it depends on the color too, which finish offers the best performance and appearance, all things considered.
Finally, there is polyurethane. I consider it the least desirable finish to use on a guitar for tone and appearance; it's very "rubbery," it surface scratches quite easily, it has a *slightly* hazy appearance even after the best polishing (best noticed under fluorescent lighting) , and even after wet sanding and buffing, a slight texture tends to redevelop after several days (due to its ongoing affinity for continued cross linking). Like polyesters, most polyurethanes are catalyzed with a hardener.
Polyurethane is what 99.9% of auto body shops use today for repairs and repaints. The only thing it has going for it, in my opinion, is that its flexibility renders it pretty tough against stone chipping and automatic car washes, a major problem with the front end of an automobile. It stands up well to harsh sunlight, and hail too. Not too much of a problem for most guitar players.
But that same flexibility is at the expense of its capacity to take a good shine with a buffer, and in the case of a guitar, to not kill the tone. A harder finish is better for anything that needs to resonate (like a guitar).
Comment from contributor G:
On a solid body, strings are anchored by a metal bridge on one end, and a plastic or composite nut on the other. The magnetic pickups detect the string vibrations and send signal to the output. So, type of wood has absolutely nothing to do with the sound of your electric. A better design (neck-thru) can give you a little more sustain because there is no joint to absorb energy. But as far as tonal quality the only thing that matters is the electronics.
My first guitar I used polyurethane and ended up fairly nice, however after blocking, polishing and buffing the finish continued to decline as all the swirls and imperfections slowly started to come to the surface (months later). That's when I researched and started using Nitro. It has all the qualities that I was looking for. Applies easily, sands and buffs wonderfully (although it can burn with power sand/buffing if not careful), and the sound is much cleaner. Nitro can be very soft during the curing process, however it also has the wonderful quality of being very easy to spot repair.
The above statement is partly true, but how the strings vibrate also depends on the things such as wood type, neck construction and etc. You have to think of it as a whole system. For instance if the strings were attached to a huge diamond (a very rigid crystal structure) the string's vibration would still be affected by it. On the opposite end the guitar would be made of a less-rigid material, like rubber. In any case, materials exhibit different responses when excited at different frequencies (modes). This is well known to acoustics engineers and civil engineers.
Finishes have a huge impact on the tone of a guitar, whether it's acoustic or electric. I really can't overstate this. I wouldn't necessarily say finish is a bigger factor than choice of wood, but I have definitely heard some very well built guitars turned to paperweights by a polyurethane or polyester finish that's simply too thick. Nitro sounds best. It really does. It tends to age with the instrument as well, giving the guitar a "broken in" or "more open" sound.
Thin polyester is, in my opinion, the next most musical choice - the thinner the better. Even with electric solidbody guitars the thicker the finish the more it damps the resonance of the instrument not only in the upper registers but through the entire frequency range. Acoustic guitars show an even more pronounced difference in tone with different finishes. Nitro covered instruments such as Gibson’s or more expensive Martin’s are louder and brighter, but also much richer in the low and midrange frequencies. They'll mature much more quickly and much more beautifully. You really don't find many French polished guitars, but I know a very talented luthier that will use a French polish for the right price (10k or more usually). I really can't say that French polish sounds better than a nitro finish and from what I understand it's extremely difficult to apply.
The trade off for real tone is durability. Nitro, when applied correctly, is very thin and will eventually begin to sink into the instrument allowing the grain of the wood to show. Most guitarists like that though. I would never recommend a poly-anything over nitro for tone.
Paul Reed Smith and Taylor guitars are both legends in the industry for their poly finishes. Both are very quick to apply, very durable, and very easy to repair. But both makers offer very high end models that are nitro finished in the interest of a more open tone. Paul Reed Smith talks quite a bit about wood and finish and tone.
Nitro really is the king. Check out an epiphone Les Paul next to a Gibson. Don't plug them in. Just play them acoustically. You'll marvel at the difference in sound and the remarkable resonance you feel when you play the Gibson. The first time I played a Gibson 1959 reissue I could tell it was out of tune without it plugged in by the vibrations I felt through the back of the neck. Hide glue and nitro all the way.
Finish counts, for sure. It makes a huge difference.
With regards to the final body's finish affecting the final tone; I agree with any comment indicating that it's really the acoustic-based instruments (a semi-hollowbody that is electrified) that would benefit from the tone offerings between densities of a Polyurethane to Nitrocellulose Lacquer. Can't argue there at all - pure physics - it matters! The resonance of an acoustic sound board obviously is affected by the density of the finish. It's not rocket science on this point. Resonance-damping materials come in all forms, and a high-weight finish is one of them! Heavy finishes kills the acoustic vibrations. Got it!
Also, with regard to any previous comment about solid-body electric guitars having not much affecting them but the neck joint - I totally agree!
We did a serious test with six accomplished guitarists, listening to our base models builds only through a blind scrim with each guitar played by the same gentleman (a famous guy too). The shapes and electronics of each guitar were absolutely identical. The only difference between them was the body's primary wood (basswood/mahogany/maple/Australian lacewood) and the finishes (unfinished/clear lacquer/polyurethane paint).
The results you ask? Well you guessed it, absolutely nobody could tell the difference in any of the guitar's amplified tone and that included the luthier and myself on top of the six test subjects.
We played them from behind an opaque scrim for two hours and no one could guess which was which. Get it? No one could identify which guitar was being played. Did we ever learn a valuable lesson that day! You should as well.
Now, to the favor of some discriminating ears there that day, a few picked up that the Australian Lacewood base model had tad more sustain (a very high density wood, thus an understandable observation), but that's it.
The case for this topic of conversation was resolved and closed for me back in 1996. It was proven to me with my own ears by others hands. I hope my comments will be taken seriously and used as a knowledgeable reference for this ongoing debate over finishes affecting electric solid-body tone.
My final word: Solid-body electrics guitars do not benefit from various finishes. It is the electronics and pickups that make the primary difference between two or more identical guitars' sound. My kind regards to all who have participated in the wonderful discussion. All the best to you and keep your comments coming!