Question about finish

Construction and repair of Classical Guitar and related instruments
LBrandt
Posts: 754
Joined: Sat Mar 26, 2011 1:40 am

Question about finish

Post by LBrandt » Sat Apr 29, 2017 12:14 am

Hello,

Can anyone describe the basic differences between a polyurethane finish, a nitrocellulose lacquer finish and a french polish finish, in so far as it pertains to benefits, durability, sound, etc?

And now, I have two more questions concerning finishes.

First, if you had your choice of finishes for the soundboard, (say there was no difference in price) would you choose french polish, polyurethane or nitrocellulose lacquer?

Second, since they say that both french polish and nitrocellulose lacquer are thinner than polyurethane and allow the soundboard to have more resonance than poly, have you ever felt that either of them actually provide too much resonance?

I ask these because I’m in the process of having to choose a finish for a guitar that I’m about to order.

I also found a website discussing a nitro finish, and according to it, a nitro finish is not durable at all and will wear away.

Louis

User avatar
Michael Lazar
Luthier
Posts: 256
Joined: Mon May 12, 2014 10:26 pm
Location: St. Albert, Alberta

Re: Question about finish

Post by Michael Lazar » Sat Apr 29, 2017 3:10 pm

1. I would choose French Polish. Nitro would be my second choice and polyurethane my third.

2. Any finish of any kind will reduce the resonance of the sound board hence none of them can produce too much resonance.

3. Nitro cellulose is generally very durable. There are many different iterations of nitro cellulose. Some are more flexible than others. The same can be said for polyurethane and other synthetic finishes.

In terms of the effect on sound and despite the many claims that french polish "sounds better" than all others, its been my experience that none are better than any other provided that the thickness of the finishes are equal from one type to the next. This being said both lacquer and polyurethane are often applied too heavily and that can impact the responsiveness of the guitar.

French Polish is more vulnerable to wear than either of the others, however, it is by far the most easy to repair and or refresh. It's also, in my opinion, the easiest finishing process for a non professional to learn to do and requires no special equipment. French polish never needs to be stripped in order to refinish all or part of an instrument. It should be noted that French Polish generally gets harder and more durable with age.

Nitro Cellulose is more vulnerable to developing cracks from temperature change and dings than either of the others and it is far more difficult to repair. In extreme cases of crazing due to a sudden change from cold to hot, the entire instrument may need to be stripped.

Poly Urethane is usually more flexible than nitro cellulose so it may withstand temperature change better. However it is the least organic in appearance and, to my eyes at least, has the appearance of a coating of plastic.

User avatar
eno
Posts: 233
Joined: Fri Dec 09, 2016 4:56 pm
Location: Boston, USA

Re: Question about finish

Post by eno » Sat Apr 29, 2017 10:48 pm

Michael Lazar wrote:2. Any finish of any kind will reduce the resonance of the sound board hence none of them can produce too much resonance.
Knowing nothing about guitar making let me ask a stupid question. If any finish reduces resonance then why put any finish at all? Lutes have no finish on the soundboard and they survive just fine.
Paulino Bernabe 'India' 2001
Rokutaru Nakade 1967
Takamine C136S and C128S
Yamaha SLG200S silent

vesa
Posts: 373
Joined: Tue Mar 01, 2016 12:52 pm
Location: Sulva, Finland

Re: Question about finish

Post by vesa » Sun Apr 30, 2017 6:47 am

eno wrote:
If any finish reduces resonance then why put any finish at all?
Dirt, grime, dust etc. whatsoever can´t easily be wiped off the surface and will gradually eat its way to tonewood remain there and after a while affect the sound. And if you accidentally pour some liquid on it will change the shape (raise grain, expand in all directions).
Somebody might also be interested in how their instrument looks = if tonewood isn´t protected at all it will look pretty awful in a very short time and remain so.
Vesa Kuokkanen

Antonio Marin nr. 813 1995 (Bouchet)
Vesa Kuokkanen 2016

Pede
Posts: 52
Joined: Mon Jan 06, 2014 11:01 am
Location: Friesland, Holland

Re: Question about finish

Post by Pede » Sun Apr 30, 2017 9:32 am

But on my baroque guitar spruce soundboard there seems to be nearly no finish at all. And that is common on lutes.
Why does it Work on those instruments and not on modern guitars?
I am curious about that.
Gert Petersen 2000, Spr-BRW
Felipe Conde FP17 Negro
Santos Hernandez 1932 S-BRW
Asturias 10 string s-IRW
Ramirez 1a Especial 2014
Bernabe M5 S
Bert Kwakkel Merula 1982
Baroque guitar by Martin de Witte

User avatar
eno
Posts: 233
Joined: Fri Dec 09, 2016 4:56 pm
Location: Boston, USA

Re: Question about finish

Post by eno » Sun Apr 30, 2017 10:35 am

vesa wrote:
eno wrote:
If any finish reduces resonance then why put any finish at all?
Dirt, grime, dust etc. whatsoever can´t easily be wiped off the surface and will gradually eat its way to tonewood remain there and after a while affect the sound. And if you accidentally pour some liquid on it will change the shape (raise grain, expand in all directions).
Somebody might also be interested in how their instrument looks = if tonewood isn´t protected at all it will look pretty awful in a very short time and remain so.
I played lute for 3 years, there was no finish but I didn't get a single scratch. I understand that the finish gives some protection but if it compromises the sound I would rather choose no finish.

Although I noticed that French finish on good handmade guitars is usually very thin, I don't think it noticeably affects the sound. As opposed to thick synthetic finish typical on factory guitars.

I think no finish makes a difference for lutes because lutes have very thin soundboards. Guitars have much thicker soundboards and thin finish probably does not affect the sound.
Paulino Bernabe 'India' 2001
Rokutaru Nakade 1967
Takamine C136S and C128S
Yamaha SLG200S silent

User avatar
Michael.N.
Posts: 6272
Joined: Sun Mar 25, 2007 7:28 am
Location: UK

Re: Question about finish

Post by Michael.N. » Sun Apr 30, 2017 10:50 am

It's usual for there to be something applied to the soundboards of lutes and baroque guitars, even though it may appear to be bare wood. Egg white, wax, thin shellac, rubbed on oil finish - it's all been used. There's just not a lot of finish applied in the first place. It was the same with romantic guitars. Things are also a little deceptive. Scratch a varnished or a full gloss shellac finish and it immediately shows large and rather very obvious. Scratch bare wood and it's much less noticeable. It's not logical to think that an unvarnished soundboard has just as much protection as one that has been varnished. It's not magic, it's simply the way that light reflects back from a glossy surface and the way that it reflects from one that is dull.
Then there's the factor of nails/no nails and of course the repertoire. Lutes tend to be played in a more timid manner although baroque guitars can receive a bit of a bashing with strumming techniques. They all suffer from wear in the area that the pinky rests. Finally lutes and baroque guitars are very delicate instruments compared to a modern guitar. Some players might just be a bit more careful when playing them even though they may not be altogether conscious of it.
Historicalguitars.

souldier
Posts: 680
Joined: Tue Dec 08, 2015 4:45 pm

Re: Question about finish

Post by souldier » Sun Apr 30, 2017 12:28 pm

eno wrote:
Michael Lazar wrote:2. Any finish of any kind will reduce the resonance of the sound board hence none of them can produce too much resonance.
Knowing nothing about guitar making let me ask a stupid question. If any finish reduces resonance then why put any finish at all? Lutes have no finish on the soundboard and they survive just fine.
I have heard luthiers that say guitars actually sounds better with some finish on it rather than having none at all. The finish takes a bit of the hard edge away and makes the sound smoother/silkier.

Go over to Douglass Scott's website. He has a blog and audio recordings of his guitars before and after French polish is applied.
Last edited by souldier on Sun Apr 30, 2017 5:32 pm, edited 3 times in total.
"Success grants its rewards to a few, but is the dream of the multitudes.
Excellence is available to all, but is accepted only by a few." - Christopher Parkening

User avatar
Michael Lazar
Luthier
Posts: 256
Joined: Mon May 12, 2014 10:26 pm
Location: St. Albert, Alberta

Re: Question about finish

Post by Michael Lazar » Sun Apr 30, 2017 2:26 pm

A lot of these things are matters of opinion and how instruments are finished are often founded on tradition. The impact of French polish on the degree of responsiveness seems to be negligible to me, however the impact upon the tonal characteristics is quite noticeable I find. I love the sound of an unfinished guitar but I love it even more when it is finished. Pretty much as described in the previous post.

Ryeman
Posts: 73
Joined: Sat Oct 22, 2016 4:31 pm

Re: Question about finish

Post by Ryeman » Thu May 04, 2017 12:20 pm

Regarding the finish, or lack of it, on lute fronts; as Michael says, there may actually be a finish, even if you can't see it.
When I made lutes I applied a finish to the fronts made up of equal parts egg yolk, water and linseed oil. Several coats were applied, over several days. The mixture was kept in the fridge to keep it from going off.
This finish sealed the wood. It stopped it going dirty. It didn't overburden or deaden the front. And it looked almost like bare wood.

Alan

fast eddie
Posts: 23
Joined: Mon May 15, 2017 4:39 am

Re: Question about finish

Post by fast eddie » Sat Jun 10, 2017 2:43 am

I have noticed that some guitars have either a matt finish or as in the case of Alhambra, has Open Pore (OP) models. I wondered how does one keep dirt and grime out of the pores of these guitars.

Jose Marques
Luthier
Posts: 107
Joined: Sun Nov 29, 2015 1:36 pm

Re: Question about finish

Post by Jose Marques » Sat Jun 10, 2017 8:02 am

my experience some years ago, wen i was studing the guitar making, i have finnished one of my guitars with nitro, it was my first portuguese guitar.

unlucky wen i send the guitar to my client, i was in Portugal and he in Luxembourg , the lovely logistics enterprize has damage the guitar, i believe the instrument was in a very high temperatures, then the finish was brake in some parts and one of the sides as well.
my cliente kept that guitar for some 2 or 3 weeks and wen he have the chance he decided to visit me and repair, at that time we decided to strip all guitar and apply shellack

the diference of sound was really amazing the guitar sounds really better then.

no in this days i can tell that this fact decided my future works, i now work with shellack and oil as well, i love the oil finish, but to use on soundboard you must be very careful and must build very slowlly.

Like lutes, in some tradicional instruments in Portugal we use only bee wax, is a orange wax you just spread a very tiny in top the thing is, we must do this time to time, for a guy that plays every day maibe 1 tipe year. This kind of finish the musitian must have some attention with the instrument, but i believe with all finishes must have carefully and atention.

i believe that for back and sides we can use other varnishes but will depend what we wish, the poly is very hard and the finish looks like plastic, but if you like thats ok, affects the sound? i believe that is does, thinks this way, in the smallman guitars the objective is block back and sides, then in this guitars is totally understandable use polyurethane... and now existes the water version for the guys that like me wishes to protect the enviroment that is a good thing :)

I saw that lots of builders at this time are using spray varnishes for back and sides and shellck on top... that can be a good choice as well..

P.S. in my opinion the oil finish for the neck is a very good choice, the touch is smooth and does not make noises wen you move your hand like a high gloss finish...

:D
I'm a Luthier living in Bury st Edmunds UK

User avatar
Alexandru Marian
Luthier
Posts: 3163
Joined: Sat Dec 23, 2006 5:02 am
Location: Bucharest, Romania

Re: Question about finish

Post by Alexandru Marian » Sat Jun 10, 2017 11:06 am

I just finished my 4th guitar with (very thin) nitro back and sides (still FP soundboard) and I can't hear any negative. As with full FP, the guitar actually sounds better than when it was bare wood.

Nitro actually seems to me to be less hard than shellac, easier to scratch. But being thicker, it prevents impacts going deep into the wood. It should also react less to chemicals.

I simply have had enough of rubbing FP like a slave even for months to achieve a deep gloss then to see it looking like it has been blow-torched by less careful or funky sweat players.

If i could turn back time, I would assemble a nitro finishing setup before buying the first saw, plane and chisel.

User avatar
Manuel Najera
Amateur luthier
Posts: 116
Joined: Wed Sep 09, 2015 6:16 pm
Location: Yucatan, Mexico

Re: Question about finish

Post by Manuel Najera » Sat Jun 10, 2017 5:40 pm

Alexandru Marian wrote:
Sat Jun 10, 2017 11:06 am
I simply have had enough of rubbing FP like a slave even for months to achieve a deep gloss then to see it looking like it has been blow-torched by less careful or funky sweat players.

If i could turn back time, I would assemble a nitro finishing setup before buying the first saw, plane and chisel.
Couldn't agree more!
I am not an expert luthier, but I have not noticed any remarkable difference on my guitars finished with shellac or polyurethane, or any other guitar I have heard/played.

I have finished guitars with:

• All Shellac
• Polyurethane on the B&S and neck and shellac only on the soundboard
• And all Polyurethane (typically when the client wants a satin finish). I still haven’t figure out how to achieve a shellac satin finish. :(

I do have to say that shellac looks more natural, so as Nitro (this one is way more harmful than poly, that is why I don’t use it).
And also have to say that I can go thinner than shellac using poly, especially if it is a satin finish (between .001 and .003”). And still end up with a more durable finish by far.
But then again, IMO non finish is better than the next, they all just have their own pros and cons, both for the luthier and the owner. Regarding acoustics, I think, well applied, they all work just fine.

Jose Marques
Luthier
Posts: 107
Joined: Sun Nov 29, 2015 1:36 pm

Re: Question about finish

Post by Jose Marques » Sat Jun 10, 2017 7:31 pm

Some of you have used the water base solution ?
I'm a Luthier living in Bury st Edmunds UK

Return to “Luthiers”

Who is online

Users browsing this forum: CommonCrawl [Bot], doralikesmath, zupfgeiger and 27 guests