"Varnish" Finish

[OddManOut]

I contacted the builder of a preowned guitar I am considering to find out if he used nitro. He replied as follows:

"I use varnish so you won't have any worries about finish checks, if the guitar case is smokin' hot from being in the sun, you might want to wait a few hours for things to even out before you take it out into an air conditioned area."

Does "varnish" mean oil varnish or are there other varnishes? I was expecting him to answer either nitro or urethane. Do modern urethanes fall into the varnish category?

I am following up with the builder, BTW. I thought it might make for an interesting discussion.

[Brent Hutto]

In my experience, guitar builders who say "varnish" do indeed mean some variety of oil varnish. Of course that still covers a lot of ground with the various types...

P.S. Or they mean catalyzed polyester that isn't actually any kind of varnish at all. Go figure. ;-)

[El Conquistador]

Hopefully Laurent Brondel will see this an chime in. He uses an oil/varnish finish that is spectacular.



LC

[Chazmo]

OddMO,

I don't think anyone would call a polyurethane (or nitrocellulose) finish a "varnish." A novice might say something like that accidentally, but not a builder/luthier.

[Diamondave]

I have oil varnish on my SEXAUER... I love it, great for tone.... Here is a pic of my guitar...

http://www.sexauerluthier.com/FT-15-07-b.html

[Broadus]

My incoming Covey has a Tru-Oil finish, which is characterized as an oil varnish. Bruce Sexauer's comments about oil varnishes made me really comfortable with it. And, no, I doubt anyone would ever call nitro or poly finishes by the term "varnish."

Best,
Bill

[OddManOut]

And here's the answer straight from the builder:

"I use what's called polyester varnish. Catalyzed, not uv cured. Larrivee used it for years before the move to California and the uv ovens. Less fragile than the lacquers."

Muy interesante...

[SteveS]

That is a great finish.

[leeasam]

here is a Collins D2H varshish model at the shop I go to for sale. Just got it in used.

[Bruce Sexauer]

Catalyzed Polyester may or may not be a great finish, but it certainly is not varnish by any definition I am familiar with.

There are those who call Alcohol based finishes varnish, but it is what I call Shellac. They are likely Violin makers, not guitar makers.

Solvent based PolyUrethane seems like a varnish to me, but there is some technical difference having to do with Polymerization. I do not understand it.

Store bought varnishes come in two main categories, short-oil, and long-oil. Most Guitar appropriate varnishes are short oil, which essentially means they dry hard in hours to days. Long-oil dries hard in months or years, if it ever really does. Cabinet varnish is short oil, Yacht varnish is long oil, generally. The difference is often Tung-oil.

Rub-on oil finishes are generally detrimental to the wood in a musical instrument as they penetrate it and alter it's character. True-oil is one of these, along with Watco and similar Danish oils. Nice looking and feeling results can be obtained, but it is generally thought to be at some cost to quality of sound and longevity. Hearsay, but it makes sense to me.

Beside the "fact" that traditional oil varnish finishes are incomparably beautiful and some of us believe they promote noticeably superior sound, they have two other terrific advantages. One is that they can be applied by hand with complete success using just a decent brush and some abrasives. No special space or expensive equipment is called for. The other is that they are much more environmentally friendly than any of their competitors except French Polish.

French polish is shellac, and it is neither adequately durable, requiring regular maintenance and extraordinary care, nor is particularly easy to attain professional results. It does have in common with oil varnish a relatively thin coating, which many consider a performance advantage.

[Howard Klepper]

There is a very broad usage of 'varnish' in the fine art world that includes just about any clear film coating. In this tradition, those film finishes such as shellac that are dissolved in alcohol are called spirit varnishes. Some in the art world might call nitrocellulose lacquer a kind of spirit varnish; there is alcohol in its mix of solvents.

In the housepaint world, 'varnish' used to mean an oil/resin combination thinned by hydrocarbon solvents in the mineral spirits/naptha category, or by turpentine. This is the usage found among guitar makers. Many of the resins used in these varnishes are synthetics such as urethane and phenolic. But urethane does not have the clarity of many of the other resins used in these varnishes. Those clarity issues seem to have been at least partly overcome in the catalyzed urethane finishes.

Waterborne finishes that behave more or less similarly to the oil varnishes in their application properties are sometimes called varnishes, too.

[Laurent Brondel]

To add to what Bruce and Howard wrote, my understanding of the term "varnish" is any finish that cures by polymerisation.

The classic shellac (or/and French polish) and nitrocellulose finishes cure by evaporation, meaning when the solvents are gone, what's left is the "finish".
The term "spirit varnish" can mean a lot of things, but mostly it is a shellac with added gums and resins (to modify elasticity, hardness and light refraction), so it cures by evaporation, but also polymerisation (it hardens more and more with time).
On a side note, very old shellac finishes tend to become impervious to their solvent (denatured alcohol), and very tough. Whereas nitro just disintegrates, perhaps slowly with the better products available now.

Oil varnishes cure entirely by polymerisation. I am not a chemist, but as I understand it, short molecules becomes long molecules when exposed with oxygen and/or UV. A short oil varnish has more resin per oil ratio, so it is tougher and harder. A long oil varnish has more oil per resin ratio, so it is more elastic and is suited for exterior work (most also have UV blockers). Woodwork on a boat or a deck tends to expand and contract quite a bit, and rapidly, a short oil varnish would just peel away after a short while.

IMO there is nothing that looks and feels better than an oil varnish, it probably has to do with how it refracts light on wood, a kind of kaleidoscopic experience. Also, as Bruce pointed out, it is pretty un-toxic as far as finishes go, and user-friendly if one is not in a hurry. It is virtually impossible to do a complete oil varnish on a guitar in less than 10 days.
It is also not too difficult to end up with a relatively thin finish (mine are always about .004"), which will not hamper the tone.
It is my opinion that whatever hard and elastic finish will not affect the tone negatively, as long as it is thin. I personally can not hear a difference between a thin French polish, nitro or oil varnish finish.
Most modern finishes tend to be around .008", sometimes .010", and it seems to me those guitars would sound much better with a thinner finish.
Also, a tung-oil based varnish thinned with turps smells wonderful…

I think it's kind of a misnomer to call modern polyurethane, urethane, catalysed or UV cured finishes "varnish". Even if they cure by polymerisation (and much faster than a short-oil varnish), the finish looks and feels nothing like an oil varnish.

[Broadus]

I know better than to get in a discussion when the experts have spoken, but from what I've gathered, Tru-Oil has been used effectively on acoustics because it does not penetrate really hard woods. Softer woods, though, require a sealer before the Tru-Oil is applied. At least that is my understanding.

Whether it fits Bruce's definition of an oil varnish or not, I do not know. Perhaps Bruce can chime in. However, Luthier's Mercantile International describes it this way:

Most oils available as wood finishes are either linseed oil or tung oil in some form, with or without any additives. Among all of the oil varnishes available for use as a simple wipe-on finish for musical instruments we offer and support the use of the Tru-Oil® product line. Tru-Oil® is a polymerized linseed oil with other natural oils added. This formulation will actually build-up as a finish unlike the raw or boiled linseed oils. The Tru-Oil® wipe-on varnish (our part FTO) and its matching Sealer-Filler (FTOS) have been used for years to finish hardwood gun stocks so its properties and application process are well known. Even though it is not as protective and durable as a lacquer finish it produces a hard, thin and flexible finish that has no detrimental effect on the tone of the instrument.

Regards,
Bill

[Chazmo]

Outstanding information, guys. I may not be getting much work done today (internal networking problems), but I surely learned something from this thread.

[Laurent Brondel]

Bill, Tru-oil is not a bad finish for a guitar. Definitely not the best though. It is substantially softer than, say, Behlen's Rockhard. It builds very slowly and IME doesn't buff as well as a "real" varnish. Light refraction is not as attractive either, IMHO.