Official Luthiers Forum!

Owned and operated by Lance Kragenbrink
It is currently Mon Jul 28, 2025 8:49 am


All times are UTC - 5 hours


Forum rules


Be nice, no cussin and enjoy!




Post new topic Reply to topic  [ 15 posts ] 
Author Message
PostPosted: Fri Apr 10, 2009 5:48 pm 
Offline
Cocobolo
Cocobolo

Joined: Tue Apr 22, 2008 4:24 pm
Posts: 148
Hello all

I got a client who came in the other day for repairs of a soundboard crack.

It so happen that he had another crack on the soundboard that was fixed by another luthier. The splint that was installed was noticeably lighter in colour than the soundboard (the guitar was built about 8 years ago), so he then took his guitar to another luthier who specialized in restoration. That luthier used a UV light on the repair to get it to darken to the surrounding colour.

I had heard and read about this technique, and was wondering if anybody here uses it. I would be interested to know, in particular, about:

-the type of light required (and where to get one)
-how close do you put it to the desired area, and how long do you let it "cook"
-how do you protect the soundboard around the area that you want to darken
-any other info on this technique that you could share.

Many thanks,

Pat


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 1:49 am 
Offline
Contributing Member
Contributing Member

Joined: Wed Mar 19, 2008 11:49 am
Posts: 897
Location: Northen Cal.
Pat,
Years ago I had though about this for furniture repair. I thought those uv lights the Dentist uses to kick off the acrylic in your teeth would work cool for this. I was thinking of using a mask of cardboard that had a hole cut in it that you hold off of the work surface similar to what you would do to feather a paint job. I heard those lights were very pricey though.
Link

_________________
Cut to size.....Beat to fit.....Paint to match.


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 10:17 am 
Offline
Cocobolo
Cocobolo

Joined: Tue Apr 22, 2008 4:24 pm
Posts: 148
Hey Link

My ex-wife was an esthetician and she used an UV light for some sort of skin treatment. I recall it wasn't that expensive (a couple of hundreds?) but I am just not sure if it had enough power to do the job. That is why I am seeking advice, so that someone may know the necessary power is for the job.

Pat


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 12:02 pm 
Offline
Koa
Koa
User avatar

Joined: Wed Sep 26, 2007 12:55 am
Posts: 1505
Location: Lorette, Manitoba, Canada
First name: Douglas
Last Name: Ingram
City: Lorette
State: Manitoba
Country: Canada
Focus: Build
Maybe a little harder to control, but there is an unlimited amount of free, high powered,UV light outside.

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 3:20 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Sat Jan 08, 2005 3:37 am
Posts: 2670
Location: United States
First name: John
Last Name: Mayes
City: Norman
State: OK
Focus: Build
Status: Professional
I used to use a blacklight box (thanks Lance McCullom!) to speed up the dry time of lacquer. It also emits a UV light and darkened the tops quite a bit. Don't know if that heps, but might give ya something else to consider.

_________________
John Mayes
http://www.mayesluthier.com


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 3:33 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Wed Jan 19, 2005 5:23 am
Posts: 2356
Location: United States
A black light works fine for this. It usually takes a few days to a week under the light to get the desired effect.


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 6:17 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Sat Jan 15, 2005 12:50 pm
Posts: 3933
Location: United States
There was a good article about UV light in the recent Violin Society 'VSA Papers' publication. The take-away message was that all of the effects produced by UV on wood were due to the prodution of ozone by the UV, which reacts with the nitrogen in the air to form nitric acid. This is basically (if you'll pardon the pun) a harmful reaction that breaks down the wood. There seems to be no way to effectively neutralize the acid once it's there.

Except possibly for some special reactions, it appeared as though anything we'd want to do with UV would be accomplished eventually by the lower-energy (and hence, safer) UV-A light that you can get from common 'black lights'. The author did not cover the use of UV to cure polyester, which may require a specific wave length to work most efficiently for all I know.

I have used black light bulbs to hurry along the drying of oil varnish. Some woods, particularly tropical hardwoods, contain enough non-drying oils to slow or nearly stop the drying of some oil varnsishes. Last spring, for example, I had problems with 'Rockhard' varnish not drying on some parts of the Macassar ebony binding on a guitar. Since I know from experience that you won't succeed with this stuff if the first coat is not fully cured, I used a small blacklight CFL and a foil lined reflector to help it along. The process took a day or two, and after that things went along as planned. Home made 'Fulton' varnish simply will not dry at all without strong UV light. Here in New England we don't get as much of that as reliably as Fulton does in the California Sierras, so a UV cabinet is a requirement here. In these cases I believe that the effects are due either to the energy of the UV photons absorbed by the varnish, or they might be from the ozone reacting directly to oxydize the monomers. Anyway, it works.

BTW, 'Rockhard' varnish flouresces under UV. So do Koa wood, and Black Locust.

The best tip I've heard of for matching the color of a splice is simply to cook the wood a little before making the splice. Of course, you can't do that once the splice is in.


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 7:17 pm 
Offline
Cocobolo
Cocobolo

Joined: Tue Apr 22, 2008 4:24 pm
Posts: 148
Hey guys

That blacklight tip is quite interesting. I told the client that I may have the time to fix his guitar in May or June (presently pretty busy with a couple of orders and making 2 demo guitars for the Montreal Guitar Show), and since his Spruce top has gotten quite dark over the years, I figure I may need the UV treatment when I fix that particular guitar, and maybe others down the line.

Would you guys care to recommend any particular types of blacklight? I have never bought one before (although I do remember crusing the bars under blacklights back in the disco days of the late 70's and early 80's :oops: ). If you just have any pointers, including retailers, I would be very much obliged!

Cheers

Pat


Top
 Profile  
 
PostPosted: Mon Apr 13, 2009 8:18 am 
Offline
Walnut
Walnut

Joined: Mon Mar 09, 2009 12:32 pm
Posts: 25
First name: Victor
Last Name: Seal
City: Trenton
State: Michigan
Zip/Postal Code: 48183
Country: USA
Focus: Build
Status: Amateur
I build fiddles and violins. I use UV "grow lights" from Walmart to darken wood and speed up drying time for oil varnish. Cheap and effective. You could mask off areas that you wanted to treat.


Top
 Profile  
 
PostPosted: Mon Apr 13, 2009 8:44 am 
Offline
Old Growth Brazilian
Old Growth Brazilian

Joined: Tue Dec 28, 2004 1:56 am
Posts: 10707
Location: United States
If you’re looking to set up a moderate to larger UV booth most pond supply stores or online shops sell 8.5" long 8watt to 50" long 65watt high intesity UV bulbs. Be carful these are very intense and can damage your eyes quickly


Top
 Profile  
 
PostPosted: Tue Apr 14, 2009 6:06 am 
Offline
Cocobolo
Cocobolo

Joined: Tue Apr 22, 2008 4:24 pm
Posts: 148
Thanks for the replies guys!

I will look into it.

Cheers

Pat


Top
 Profile  
 
PostPosted: Tue Apr 14, 2009 2:18 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Tue May 02, 2006 9:02 am
Posts: 2351
Location: Canada
First name: Bob
Last Name: Garrish
City: Toronto
State: Ontario
Country: Canada
Status: Professional
Alan Carruth wrote:
There was a good article about UV light in the recent Violin Society 'VSA Papers' publication. The take-away message was that all of the effects produced by UV on wood were due to the prodution of ozone by the UV, which reacts with the nitrogen in the air to form nitric acid. This is basically (if you'll pardon the pun) a harmful reaction that breaks down the wood. There seems to be no way to effectively neutralize the acid once it's there.

Except possibly for some special reactions, it appeared as though anything we'd want to do with UV would be accomplished eventually by the lower-energy (and hence, safer) UV-A light that you can get from common 'black lights'. The author did not cover the use of UV to cure polyester, which may require a specific wave length to work most efficiently for all I know.


Is there a way to access the paper online? I may be missing something, but the nitric acid thing sounds a little fishy. UV light pops bonds on things and oxidizes them, but making nitric acid directly from nitrogen and oxygen gas wasn't something I thought was possible without extreme temperatures and/or pressures.

The UV lights they use for curing finishes are very specific wavelengths. I forget which, exactly, and I've heard there is some debate on which exact frequency works best.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services


Top
 Profile  
 
PostPosted: Wed Apr 15, 2009 2:57 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Sat Jan 15, 2005 12:50 pm
Posts: 3933
Location: United States
Bob Garrish asked:
"Is there a way to access the paper online? I may be missing something, but the nitric acid thing sounds a little fishy. "

I looked in all the usual places, and can't find the issue: I may have loaned it to a student, so I'm working from memory. Again, the sequence was UV+3(O2)->2(O3)+N2-> 2(NO)+2(O2) and the nitric acid follows from there. It may take much less pressure and lower temps to produce NO with ozone, which is far more reactive than O2.

"The UV lights they use for curing finishes are very specific wavelengths."

I'm sure that's the case for the UV cure polyesters. The energy required to kick the reaction is probably known, and the coresponding wave length easy to calculate. In the case of a common varnish I'd imagine things are a little messier, since the chemistry is probably not as nicely controlled.

If the article is not on the VSA website I'd imaging you would need to join to get it, or else look up a memeber who didn't loan the issue out.


Top
 Profile  
 
PostPosted: Wed Apr 15, 2009 5:28 pm 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Tue May 02, 2006 9:02 am
Posts: 2351
Location: Canada
First name: Bob
Last Name: Garrish
City: Toronto
State: Ontario
Country: Canada
Status: Professional
Alan Carruth wrote:
Bob Garrish asked:
"Is there a way to access the paper online? I may be missing something, but the nitric acid thing sounds a little fishy. "

I looked in all the usual places, and can't find the issue: I may have loaned it to a student, so I'm working from memory. Again, the sequence was UV+3(O2)->2(O3)+N2-> 2(NO)+2(O2) and the nitric acid follows from there. It may take much less pressure and lower temps to produce NO with ozone, which is far more reactive than O2.


If they're going with that sort of sequence, then they took a leap they weren't allowed to (they only balanced the atoms, not the heats in the reactions). Elemental nitrogen (N2) is extremely stable and there are essentially no reactions with anything at standard temperature and pressure. To get it to spontaneously react with oxygen, ozone or not, they'd need to pop a triple bond and that requires insane energy (>2000 degrees Celsius!). I guess we're back with oxidation.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services


Top
 Profile  
 
PostPosted: Fri Apr 17, 2009 11:07 am 
Offline
Brazilian Rosewood
Brazilian Rosewood

Joined: Sat Jan 15, 2005 12:50 pm
Posts: 3933
Location: United States
That wasn't their reaction sequence, it was mine. I know that energy is needed to make it go. I also know that a photon of UV carries quite a lot of energy, and things like surface effects can alter the way reactions run. You do have a catalytic converter on your car, n'est ce pas? ;)


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 15 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 8 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
phpBB customization services by 2by2host.com