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guitar finish

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brian f
(@brian-f)
Estimable Member
Joined: 18 years ago
Posts: 122
Topic starter  

can anyone help me understand the differences between different guitar finishes, polyester, polyurethane, and nitrocellulose laquer.
My main interest for this is acoustic guitars, but I suppose the same differences would cross-over to electrics as well.

Do the nitro finishes offer better tone?
Do the poly finishes dampen tone or resonance or sustain?
Do the poly finishes keep the wood from aging and "opening up"?
If I want a guitar to last me for the next 40 years, is there some trade-off between durability and tone?
Are the nitro finishes that much easier to repair?

Thanks!
B


   
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slejhamer
(@slejhamer)
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Joined: 18 years ago
Posts: 3221
 

More experienced folks like Ricochet, Racetruck and Gnease can chime in, but this is my understanding:

Spray nitro outdoors and every bug and bird within a 100-yard radius will drop dead. If you are indoors, you'll definitely want to use a good respirator rated for chemical vapors. Well, you probably want to use a similar respirator even if you are outdoors, and even with the poly types ...

The advantage to nitro, from a DIY perspective, is that it's self-leveling and "melts" into the layers below, making it easy to get a smooth finish and easy to make repairs. A disadvantage, apart from the death and destruction, is that it takes a long long time to cure. Weeks or months.

Nitro supposedly flexes more than the poly finishes, thus allowing the wood to vibrate more. However, there have been posts around the internet suggesting that very thin poly finishes do not have much negative effect. It's the typical thick finish you see on low-end guitars that makes them sound like plastic.

Here is what Taylor has to say about polyester and polyurethane:
What kind of finish does Taylor use on its guitars?
Since 1995, we've been using a polyester finish which is cured by ultraviolet light. This UV-finish has many advantages over the polyurethane and lacquer-based finishes previously used. It contains as many "solids" as thicker finishes, so a thinner application provides the same protection while allowing for better tone production. It also is clearer, so the wood grain is more distinct; is more user-friendly; is much easier to sand; is more flexible; doesn't produce any cold-checking [see following question]; allows for aging; and requires a fraction of the curing time (three 23-second passes through the UV oven, versus several days using the old method). Also, because polyester is about 85 percent resin and only 15 percent solvents (almost the exact reverse of the polyurethane ratio), UV-curing it produces a greatly reduced VOC rate - the measure of the "volatile organic compounds" released into the airstream. This environmental bonus earned Taylor Guitars a commendation from the San Diego County Air Pollution Control District.

Personally, I'd use Tru Oil for a project. It's relatively safe, it's easy to apply (wipe on), easy to repair, doesn't muck up the tone, and is reasonably durable. It's the only oil based finish supported by Luthiers Mercantile.

If you want a guitar to last, treat it well and keep it humidified during dry seasons, and relatively dry during wet seasons.

"Everybody got to elevate from the norm."


   
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Ricochet
(@ricochet)
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Joined: 20 years ago
Posts: 7833
 

That's a good discussion.

Another finish that's good for DIYers, not generally available on production guitars, is shellac. Nitrocellulose lacquer is a cheap substitute for it. :D

Go over to http://frets.com/ and read Frank Ford's pages on "French Polish" if you want to read how to do that right.

Tonal effects of finishes have been greatly exaggerated. It's got to be globbed on mighty heavily to make any difference.

"A cheerful heart is good medicine."


   
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brian f
(@brian-f)
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Joined: 18 years ago
Posts: 122
Topic starter  

thanks for the info. While I wasn't really asking from a DIY perspective, It won't be long before I am, so its good info to have.
The only thing I've built is a ukulele. I used Tru-oil on that and it worked great.

I've done some readiing on other forums about the nitro vs poly debate, and it seems like its a debate that will go on forever with no clear answer ever found. I think Ricochet's comment sums up what I read, and that is that you need to glop it on pretty thick, whatever it is, before it makes a difference.

It's funny, this debate on other forums get pretty heated and ugly. Makes me really appreciate the respect that GN members have for each other's opinions. Other forums should take note.

I guess its the same answer as a lot of other debates on materials....if it sounds good, it sounds good. if it doesn't, it doesn't.


   
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Ricochet
(@ricochet)
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Joined: 20 years ago
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I guess its the same answer as a lot of other debates on materials....if it sounds good, it sounds good. if it doesn't, it doesn't.
Couldn't have said it better! :D

"A cheerful heart is good medicine."


   
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CitiZenNoir
(@citizennoir)
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Joined: 16 years ago
Posts: 1247
 

Hi :D

While I agree that whatever sounds good to you, sounds good....
I prefer lacquer finishes on my guitars.

Nitrocellulous lacquer is a highly volatile plant based (mostly cotton) lacquer.
Nitrocellulous is a primarily cotton based resin derived from a nitrating process.
(Highly volitile as it's about the same thing as the explosive kind of Nitrocellulous found in flash paper & gun cotton)

In the paint, Nitrocellulouse resin is disolved in solvent.
Adding Lacquer thinner to it makes it 'thinner' or less viscous and easier to apply by spray gun.
The solvent then evaporates, leaving the resin and solids (colors) behind.
The finish can then be sanded and polished to a high sheen.

Nitrocellulouse lacquer is gererally hard, yet flexible. Unlike Acrillic (plastic based) lacquer which is usually hard and brittle.

Shellac is derived from the secretions of the Lac insect. (Which is what the original 'lacquers' were - shelLAC and LACquer)
Sticky secretions used by the female lac insect to grab hold of tree trunks.
The color of the shellac is influenced by the sap consumed by the female insect at the time of harvest.

Either Nitrocellulous lacquer or shellac is a natural finish.

Polyurethane on the other hand is anything but natural.
It's a two part plastic catylized system (much like plastic body filler, ie. Bondo)
No thinner or reducer is used.
When the two parts are combined, they produce a chemical reaction that ends in a hardened plastic finish.

If DIY w/polyurethane.... actually supplied oxygen is recomended over a respirator. And covering the skin
completely is also a must as any overspray landing on the skin will soak into the blood stream.
Polyurethane has a large amount of Isocyanate in it.
Isocyanate, once in the lungs, will stay there forever, reducing lung capacity and causing asthma.
Also, Poly overspray will stick to everything that it lands on. Caution must be used if no spaybooth is available.

As I've said, lacquer can be sprayed on very thin (if you're good at spraying)(if not, mistakes can be sanded out)
Polyurethane is not thinned and usually requires about three coats. ( a dust coat/med wet coat/wet coat).
And as the thinner in Lacquer will 'eat' into the previous coats - bonding it (or if sprayed on enamel, will lift it),
Polyurethane HAS to be sprayed before hardening occurs.
Each coat 'melts' into the one before it making it possible to 'flow' it out at about the 3rd coat for a nice smooth finish.

At any rate - I have two Strats.... One with a Poly finish, the other with a Nito finish.
The Nito finish is by far the best sounding.
Though you are correct. There will never be a definitive answer to the question as to which is a better finish for guitars,
or which yields a better tone.

My Strat with the poly finish still looks brand new. And believe me, I haven't exactly been treating it well.
It's my player guitar.
It has no crazing or discoloration after 20 years of abuse.
If it had been nitro - well, it would most certainly be all crazed (cracked) and (being as it's Olympic White) would be a beautiful amber color by now.
Those two 'undesireable' factors of having Nitro Lacquer on guitars, I happen to really dig 8) :D 8)

If you have lacquer, it will wear off easily, discolor, and crack (especially due to temp/humidity changes)

Poly - maintenance free.

To each his own :wink:

Ken

"The man who has begun to live more seriously within
begins to live more simply without"
-Ernest Hemingway

"A genuine individual is an outright nuisance in a factory"
-Orson Welles


   
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