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French polish cracking--have you seen it?
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=12168		 Page 1 of 2
Author:  John Elshaw [ Thu May 24, 2007 6:56 am ]
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Here's something I haven't seen before. My neighbor has a 2004 Blackshear classical guitar all french polished. There are some typical dull spots where the FP is worn, especially on the back where it touches the body. The front however is really strange, it has big cracks all over it. The cracks look almost identical to what you would call finish checking like you might see on an old 1960's Gibson for example. The spot where the arm touches the top is really bad. In this area, it's more than just finish checking, the cracks are actually about 1mm wide and there is a noticable depression along these lines.

Has anybody else ever seen this, and if so, do you have any idea what could cause it? It really looks worse than normal wear, especially for a 2004 guitar.

Thanks!

John
Author:  John Elshaw [ Thu May 24, 2007 6:58 am ]
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One more thing I forgot to add, the guitar was like this when he got it 6 months ago, so it all occurred before he got the guitar, and it really hasn't changed since he got it.
Author:  John K [ Thu May 24, 2007 7:39 am ]
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Yes
   I recently had a guitar french polished by a person who has a good reputation doing this kind of work and after several months in my shop, sitting in the case, the guitar developed cracks that reminded me of old lacquer cracks. I took a heat gun and stripped it. I am sending it to Tony Ferguson for one of his super thin catalyzed urethane finishes. The shellac mystique has lost some of its allure around here
Author:  Mike Collins [ Thu May 24, 2007 7:56 am ]
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Tom applies as much finish as he can at a time.
He has told a list that I'm in with him that he can do a whole guitar start -to stop in 8 hours.

The problem is you can NOT apply any finish over uncured finish.
the crazing your friend is experiencing is the end result of applying to much to soon!
The alcohol in the underlayers need to ecsape(to help the finish dry)

Call Tom-he'll probably disagree but it need to be fixed !



Mike Collins
Author:  Michael Dale Payne [ Thu May 24, 2007 8:31 am ]
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you beat me to it Mike. You hit the nail on the head.
Author:  Mike Collins [ Thu May 24, 2007 10:28 am ]
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Hey Mikey ;
Thanks for the backup !!!!!
Sometimes I wonder if I know anything at all!
just ask my wife!!

Mike
Author:  Barry Daniels [ Fri May 25, 2007 1:06 am ]
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So the one-day french polish method developed by Brune and further promoted on Robbie's video is not recommended, I take it.
Author:  JJ Donohue [ Fri May 25, 2007 1:22 am ]
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Good point Barry! I'm watching this thread with great interest. I have done 4 so far but have not noticed any cracks as described above. For the most part, I followed Robbie's technique...except it took me a week until I was satisfied with my results. How long after finishing did the cracks appear?

I'd love to hear from those who have taken the Brune course. I have to believe that they have an alternate explanation.

Oh...and BTW...who is Tom?
Author:  Dave White [ Fri May 25, 2007 1:24 am ]
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[QUOTE=JJ Donohue]
Oh...and BTW...who is Tom?[/QUOTE]

JJ

I assume it is Tom Blackshear who made the guitar refered to in the original post.
Author:  JJ Donohue [ Fri May 25, 2007 1:27 am ]
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D'OH...thanks, Dave
Author:  SteveCourtright [ Fri May 25, 2007 1:29 am ]
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I have seen one of Brune's flamenco instruments in person, which traveled hard on the road, in a car trunk in the South and even after many months and miles seemed to be holding up very nicely indeed. So it is not so simple a diagnosis as one set of techniques making a good finish and another failing utterly. So one cannot dismiss either Brune or Robbie. My first FP instrument I used Robbie's method to good effect and so have many others.

FP is a proven finishing technique with some well known disadvantages and well loved results. In the end, you just have to try it and develop some sensitivity to the process, observe carefully and adjust accordingly. Personally, I love the look and feel so much, I am willing to put up with the idiosyncrasies!
Author:  JJ Donohue [ Fri May 25, 2007 1:56 am ]
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I assumed that Barry's comment was "tongue-in-cheek". I believe that the logic leap was made earlier in the thread.

Good point on the "chain of custody" argument, Hesh!

If Robbie's & Brune's method was the cause then I should have seen something bad in 4 guitars. No signs of cracking so far after as long as 1 year!
Author:  Michael Dale Payne [ Fri May 25, 2007 1:57 am ]
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Good Thread.

a couple years ago I tried and experiment. I took 2 serving trays I built to use a Genia pigs. I sprayed 6 light coats of 1.5#cut shellac on each. On the first one; as soon as each coat was dry to the touch I sprayed the next consecutive coat. on the other I allowed each coat to cure 24 hours. After all the shellac was sprayed on I did two more session on each, but this time I used FP technique to apply the shellac then glazed each as if they had been French polished for the start.

The intent of the experiment was to try a quick build technique I had been told about. And for the most part all worked very well and produced a near FP looking finish.

The unexpected part came some time after the experiment when the tray that the spray buildup went on rapidly developed crazing or cracking. All I could figure out caused the problem was that the tray that had the quickest spray schedule had not flash off significantly between coats since they both used shellac from the same batch cut.
Author:  JJ Donohue [ Fri May 25, 2007 2:16 am ]
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Michael...as one of your dedicated students who has hung on every word you ever had to say about FP, I beg to differ with your test.

If you were to do a similar test and used the FP application technique for each side of the experiment, I believe it would be more meaningful.

IMHO, all I can conclude from your test is to not SPRAY 6 consecutive coats before allowing to cure. Spraying lays down a significantly greater amount of shellac than the FP method. You and others have always preached the "less is better" technique of applying shellac. Now...if we knew for sure that the guy who finished this guitar sprayed as you described, then we may be on to something. Do we know that?

As far as FP goes...I'll continue to follow your masterful advice!


Author:  Michael Dale Payne [ Fri May 25, 2007 3:10 am ]
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I think you miss under stood. My experiment had nothing to to with the cracking issue initially. I was just trying a finish process that a furniture maker I know used, and trying to determine if I quickened the pace of the spray schedule, or if it cause issues.

It was months after this that the one produced cracks.

I was just pointing out that when solvent has not gassed off well it can cause shellac to crack. but the experiment had nothing to do with proving that assumption.

You are right; If I was trying to prove that this is the issue with this guitar, I would need to french polish to prove for this scenario.

I was just saying that any shellac finish if properly gassed off between sessions is a very elastic finish and not prone to cracking, but that I have run into a case where applied in a way that did not allow to gas off between session that have caused cracks
Author:  Michael Dale Payne [ Fri May 25, 2007 3:14 am ]
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[QUOTE=MichaelP] I think you miss under stood. My experiment had nothing to to with the cracking issue initially. I was just trying a finish process that a furniture maker I know used, and trying to determine if I quickened the pace of the spray schedule, or if it cause issues.

It was months after this that the one produced cracks.

I was just pointing out that when solvent has not gassed off well it can cause shellac to crack. but the experiment had nothing to do with proving that assumption.

You are right; If I was trying to prove that this is the issue with this guitar, I would need to french polish to prove for this scenario.

I was just saying that any shellac finish if properly gassed off between sessions is a very elastic finish and not prone to cracking, but that I have run into a case where applied in a way that did not allow to gas off between session that have caused cracks[/QUOTE]

I should also say that in 30 some odd years of FP finishing I have never had a FP finish crack on me with the exception of and end table that set for years nest to a west exposure window and on where the setting sun baked the table to a crisp.
Author:  SteveCourtright [ Fri May 25, 2007 3:24 am ]
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Maybe it is obvious, but just to state the cause of the cracking problem, I am sure we will agree, cracks develop because the (shellac) film shrinks as the solvent evaporates.

I have also seen finish crack because it did not adhere to the substrate - for whatever reason. Not likely with shellac from what little I know of the stuff.

Author:  charliewood [ Fri May 25, 2007 3:39 am ]
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[QUOTE=Hesh1956] [QUOTE=BarryDaniels] So the one-day french polish method developed by Brune and further promoted on Robbie's video is not recommended, I take it.[/QUOTE]

This statement sounds like a leap to me that I do not understand how it can be justified. Although Robbie and Marshal Brune do provide a fast-track French polish method this does not mean that we have any idea exactly how the builder in question French polished this particular guitar AND exactly with what..... We also do not know the entire chain of custody in terms of how the guitar was treated in the last couple of years since it’s birth.

I find it alarmist to imply that some very well respected industry contributors should now have their methodologies invalidated based on this single post and how little we in fact know........

[/QUOTE]

I think that Michael Collins establishes that Tom Blackshear the guitarmaker in question here - was quoted as saying that he applies as much polish in one sitting as possible(in a circulation that he recieved).
Thats where the technique of Robbie and Brune come in here as they also advocate this method, this essentially ties them to the guitar in question by association.
Now granted no-one seems to know how the guitar was treated throughout its life from inception -
However, it has been noted that this type of finish problem can occur when the finish is applied in such a hasty manner.. quite possibly.
This has yet to be proven - and it has only been noted I think in reality... and granted nobody should have thier methods dismissed in one fell swoop, although if rapid application is the culprit, I put forth that perhaps it may be in conjunction with other factors in play at the time of finish application, such as humidity, or perhaps the actual brand of finish may be to blame - who knows for sure at this point?
It does deserve a closer look - no doubt...
I agree good topic!
Cheers
Charliewood
Author:  John Elshaw [ Fri May 25, 2007 6:24 am ]
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Hi guys, let me give a little more information. I've been away from the computer today and am just catching up. The back and sides of the guitar look great, no checking or cracking at all. The top has some random checking all over, but right where the arm touches the instrument it is really bad with the deep wide cracks I described above.

I didn't want to bias the possible answers by suggesting an idea earlier, but here's what came to mind. The checking looks just like checking on an old lacquer sprayed guitar. My initial thought is somebody sprayed lacquer over the FP and that's why the checking looks the same. The severe cracks are where the arm touches like I mentioned in my original post, and that doesn't explain applying too much shellac too fast. If that were the case, you would think you'd see it on the back and sides as well. Also, why would the area where the arm touches gas more severely than the rest of the top?

One other thought and I have no idea if it's related--the top of the guitar is shinier and smoother than any other FP I've ever seen. I questioned whether it was actually FP or not, but the guitar was bought from Brune's shop and with all their expertise (Marshall included), I can't imagine they would confuse lacquer with FP, or with something else. Any other ideas?

John
Author:  Michael Dale Payne [ Fri May 25, 2007 6:30 am ]
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Could it be a hybrid lacquer top FP back and sides? Na!! That would be backward from what a Hybrid should be FP top and nitro back and sides.
Author:  crazymanmichael [ Fri May 25, 2007 6:34 am ]
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method of application is just one possible contributing factor, and since we don't actually know how it was applied, nor how thick the finish is, such definitive attribution of the problem to any specific application methodology is naught but pure uninformed speculation.

other factors, including, for instance, exposure to sudden extreme environmental changes can cause finishes to crack. sustained exposure to extreme cold, such as a car trunk in a northern winter, in an aircraft baggage compartment, etc., is another possible culprit.

there is no way any definitve statement of cause can be made without information which is simply not available.

fortunately it is not a terribly difficult problem to fix.
Author:  KenH [ Fri May 25, 2007 1:26 pm ]
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I may be mistaken, but if this is truely a FP top, the finish on it should be dissolvable with some alcohol. It should be easy enough to tell what kind of finish it is.


ALso, you are saying that the crackin is heaviest where one's arm would rest on the guitar while playing. After seeing what my case did to my FP on my recent guitar, I could believe that some of the clothes that the preformer wore while playing might attribute to some of this problem. In my case, the finish looked like it "melted". Keep in mind that this is a fairly fresh finish on mine VS an older finish on your guitar.


Just some thoughts on what may be happening to your guitar.
Author:  JJ Donohue [ Fri May 25, 2007 11:58 pm ]
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John...Why not contact the builder and see if he can shed some light on the issue. So far it's just been a guessing game with far more conjecture put forth than facts uncovered.

I'll be interested in what he has to say.

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