Official Luthiers Forum!
http://www.luthiersforum.com/forum/

Dark colored acoustic guitar, a challenge...
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=40040		 Page 1 of 1
Author:  jeangiroux [ Fri Apr 12, 2013 7:45 pm ]
Post subject:  Dark colored acoustic guitar, a challenge...
Hi everybody,

I'd like your inputs for this project I'm working on. I've set to build three replicas of a guitar that's in a local museum which belonged to a famous poet/songwriter from Quebec. The guitar is a nylon string Guild Mark 1 from the sixties and is rather unsophisticated in detail. It matches very closely the Hauser/Torres plan. Some pictures are attached. As you can see the guitar is a dark burgundy color... It is an all mahogany guitar, but I'm using khaya (African mahogany) for the project.

I'm looking for help on how to address the stain/dye part. I've procured some aniline based stain from LeeValley (56Z03.06) and the color match is great on some test pieces. I plan to build the rosette in place in the top, ideally on a flat board before assembly as there are some marquetry pieces that would looked better if a router pass made before adding the other rings. Furthermore, the guitar edges have no bindings just a slight round over. The guitar is finished with a semi-gloss clear. I also favor modern water based or traditional finishes(french polish or danish oil).

The steps required (in disorder) are then: seal, apply stain/dye, route for rosette, assemble rosette, grain fill (black dyed dry wall compound), assemble guitar, round edge, sand, final clear....

My plan is to:
sand and seal top with shellac
sand to 320
route and inlay rosette marquetry and rings
level rosette and seal rosette
mask rosette :(
assemble guitar
round the edge
sand and seal the rest of the guitar
grain fill with black dyed drywall plaster
level and final sand
clear with Aqualac 2

How would you go about this? In which order would you tackle the steps?

Thanks in advance!

Jean
Author:  Greg B [ Fri Apr 12, 2013 10:03 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
IMHO you'll never get that old fashioned dichroic look by staining. Nevertheless, traditionally stain would come before grain filling, or sometimes concurrently. This is a would be difficult if you use something other than oil based paste filler. Sealing before staining only works if it's a super thin coat, like a 'stain conditioner'. On mahogany, this isn't necessary, or even a good idea. But if you are dead set on black pore filler, maybe it's best.

Personally, I would grain fill with a dark paste filler. Follow that with garnet shellac french polished until it is done. Maybe do a very light stain beforehand if that isn't dark enough.

Definitely test on scrap before beginning.

Honestly I don't know what the story is on this Guild, but it doesn't really look stained. Most american guitars are finished with lacquer. If it's dark, often a tinted coat is used - either in conjunction with stain, or without stain.
Author:  B. Howard [ Sat Apr 13, 2013 6:26 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
There is not any stain on guitar you are copying, that is the natural color of the Mahogany after exposure to light for some years. Mahogany is photo-reactive and darkens considerably with exposure to light and the lacquer ambers with age so between the two this is the color that develops. If you wish to try and recreate the color on a new piece I would use a shader coat in my finish.I also would not use drywall compound as my grain filler, use an epoxy or a traditional paste type filler.
Author:  Tom West [ Sat Apr 13, 2013 8:25 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Jean: I tend to agree with Brian. I have a Mahogany guitar here at the computer that exhibits just about the same color and it is only a couple of years old. It just has Zpoxy fill and nitro finish.
Tom
Author:  Dave Stewart [ Sat Apr 13, 2013 9:02 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
FWIW Jean, one of the best treatments for mahogany is a dilute solution of potassium dichromate. Definitely an "old world" approach, it's a chemical that reacts with the tannins in mahogany (and other woods for that matter) and in the case of mahogany beautifully deepens & enriches the colour. I've used it on quite a few pieces of furniture & on a recent Honduran mahogany guitar.
Author:  LarryH [ Sat Apr 13, 2013 9:32 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
B. Howard wrote:
There is not any stain on guitar you are copying, that is the natural color of the Mahogany after exposure to light for some years. Mahogany is photo-reactive and darkens considerably with exposure to light...


I drove home from the wood store yesterday with some Honduran strapped to the roof of the car with a surfboard rack - 10 - 12 minutes max. I unstrapped the wood and there were very visible lighter lines where the straps had been - in 10 - 12 minutes of sun exposure. Just thinking that you could try some sun or UV exposure (the violin guys have special UV boxes set up for this reason) to speed up the process, avoiding the nastiness that leaving a piece of wood out in the sun can create. I'm going to experiment with some Hog sets I have coming and see what effects I might create.
Author:  Ken Franklin [ Sat Apr 13, 2013 9:59 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Dave Stewart wrote:
FWIW Jean, one of the best treatments for mahogany is a dilute solution of potassium dichromate. Definitely an "old world" approach, it's a chemical that reacts with the tannins in mahogany (and other woods for that matter) and in the case of mahogany beautifully deepens & enriches the colour. I've used it on quite a few pieces of furniture & on a recent Honduran mahogany guitar.


That's a beautiful enhancement to the mahogany, Dave. If you choose to go this route, Jean, know that the potassium dichromate requires very careful handling. http://en.wikipedia.org/wiki/Potassium_dichromate
Author:  Dave Stewart [ Sat Apr 13, 2013 10:54 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Absolutely Ken, good point. I've used it for years with no problem but it needs proper respect. (One problem is that a glass of it looks exactly like a glass of orange Koolaid! ... but is fatal several times over!)
Author:  jeangiroux [ Sat Apr 13, 2013 11:01 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Many thanks to you all for these replies which enhance my knowledge of mahogany. I'll put a piece of scrap in a sunny part of the house for a while. I'll do some searching around for potassium dichromate and get some garnet shellac. Going back to the picture stack we have taken at the museum, and looking in more details at wear areas, I guess I got mislead by the my impression of the absence of any cracks or chips in the finish. If you take a look at the attached pictures it looks like the finish is actually tinted and maybe had been touched up close to the fretboard.

Dave:
Where do you procure the Potassium Dichromate?
Do you pore fill after, if so, how?

Thanks again to the group

Jean
Author:  LarryH [ Sat Apr 13, 2013 11:09 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
jeangiroux wrote:
I'll put a piece of scrap in a sunny part of the house for a while.
Jean


And try one outside, windows can block UV radiation.
Author:  Dave Stewart [ Sat Apr 13, 2013 1:46 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
jeangiroux wrote:
Dave:
Where do you procure the Potassium Dichromate?
Do you pore fill after, if so, how?

It's been twenty years or more but I remember having to go to a chemical supply house to get an aspirin sized bottle of PotDi crystals..... don't recall the name. Pore filling can be done after... Zpoxy or whatever.
Author:  jeangiroux [ Sun Apr 14, 2013 9:21 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
I ordered the potassium dichlorate at

http://www.shellac.net

as well as the garnet shellac flakes. The sample board is in the sun, if it ever shows up...

I'll post result back here

Thanks all

Jean
Author:  Clay S. [ Mon Apr 15, 2013 9:44 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Potassium permanganate is another strong oxidizer which can also be used to oxidize finishes, may be a bit less poisonous than potassium dichromate, and is generally available at pool supply places.
A friend of mine had a 70's guild mark 3, which he refinished. If memory serves me right much of the red of the back and sides was in the lacquer.
Author:  jeangiroux [ Wed Jan 15, 2014 7:53 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
As promised, here the outcome of the project:

We applied the bichromate to the Khaya. This yielded a nice honey color, but not the red we're after. I then ended up tinting pre-catalyzed lacquer to match the end-color. I guess that the oxydation process insured that the color will be stable in the long run.

We tried our best to match the color from the pictures, then ran some samples. We returned and took more pictures of the samples side-by-side with the guitar to remove as much as possible the lighting component. In the end, we did lack a bit of red and ended up with the rosette a bit bright, as you can see in the picture.

It was fun project and thanks to everyone for the help.
Author:  Clay S. [ Wed Jan 15, 2014 8:19 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Nice!
Author:  jeangiroux [ Wed Jan 15, 2014 9:34 pm ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Thanks for your help. You were right about the lacquer!
Author:  Spyder [ Thu Jan 16, 2014 1:08 am ]
Post subject:  Re: Dark colored acoustic guitar, a challenge...
Just out of curiosity, it was mentioned that the chemicals worked with the tannin in the wood to darken it. Have you tried the old simple home made variety of vinegar and rust? Put some white vinegar in a jar, and add some rusty iron. Nails work, steel wool works even better. Just drop some old rusty steel wool in the vinegar and let it sit for a week. Makes a natural chemical that is very benign, but reacts like crazy with tannin.

You get the same effect as those black streaks you see under nails on outdoor wood fences and what not. The stuff will turn red oak black, and since it is a chemical reaction, it works on contact. Pretty neat.

Only downside is while the stuff is making, one of the byproducts is hydrogen gas. So be careful how you seal the container. When I make a batch, I make it in an old jar, cover it with plastic wrap with a rubber band around it, and sit it on the porch. When it's done, take the plastic wrap off (but not while smoking!) and you're good to go.

Never tried it on mahogany though, might be interesting to see what it does.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/