Blackwood Stain.

[woodrat]

I was wondering what various strategies members employ to either get rid of the horrible blue green stain that Backwood gets when you put it in the side bender. I usually just scrape it out but it is mainly in the area of the cutaway area that I have thinned to 1.5mm to get around the venetian cutaway section and I dont want to thin it much more. I was wondering if oxalic acid would be useful as a treatment?
Any advice would be appreciated....

Regards

John

[auscab]

Hi John ,
I'm not sure about the blue green stains but Oxalic acid works 100% on oxide stains left from metals on a lot of timbers, most that I have seen are black.
I have a large sack of the pure crystal here and would send you some but I don't think it can be posted.

[DarwinStrings]

I use oxalic acid for many stain removal jobs on wood and it does work good. Your best bet would be to stain up a bit of scrap about the same thickness and do a test run. Be careful with it cause if you leave it on the wood too long it can sometimes degrade the woods surface making it furry then you have to scrape anyway.

Jim

[Allen]

Best bet is to not get the stain in the first place John. Next time around isolate the Blackwood from any metal contact with kitchen paper or that brown butcher type paper that Stewmac jams in boxes or some cloth.

My first Blackwood build had that stain go so deep I spent days trying to sand it all out. Now I don't get any at all.

[woodrat]

Hi Allen, I had two layers of thin brown paper (thinner than the StewMac paper you mentioned) between the steel and the blackwood...it still did it
it is not as bad on the outside surface but I hope that it is not all the way through the cutaway section.It is only an issue in the cut away but the cutaway was only 1.5 mm thick to ease the bending....

Thanks Allen

John

[Allen]

I also changed from steel to alloy flashing for my bending slats. That seems to have helped a fair bit as well. Also almost no water. I just barley dampen the sides and then squeegee them damp-dry.

[woodrat]

Roger That Allen, I used too much water....I am a bit paranoid about the tight bend...I wanted it to bend easily...seems I used too much...Still hoping it will scrape/sand out.I will glue some doubling veneer on the inside.

Regards

John

[Steve]

I also wrap in paper, use alloy flashing & got staining on my last set of blackwood sides too. I gave them a light spray, but I'm going to be giving them a wipe off next time now too - thanks for the discussion fellas.

[Kamusur]

Does distilled water work?


Steve

[Allen]

Works to make steam, but it's not the water itself that makes the stain.

If I'm bending on the pipe I won't use water at all unless the piece is a bit stubborn.

[nnickusa]

Good thread for me, as my next one is blackwood....

If I'm reading this right, you just spray the sides before bending?

And, Allen, do you mean that you bend the blackwood dry?

[P Bill]

I'm relieved to hear someone else thins the side to make the cutaway bend. I haven't seen it come up before.

[Allen]

If you read through Benedetto's book on arch top guitars he tells you to take them down to around the 1.8mm if memory serves me. Doesn't reinforce them after either as the area in the bend is stronger than that on the flats.

[Kamusur]

Sorry Allen so not using water and bending dry leaves them without stain?

Steve

[Kamusur]

Allen
I have also been skeptical about using softening agents (soap or alkaline products) with the water spray (for sides) thinking it may leave residue in the wood that may cause problems for finishing/pore filling adhesion, have you got any feedback or thoughts about that?

Thanks Steve

[nnickusa]

The main reason I ask is that in Kinkade's book, he recommends soaking rosewood before bending. Now, not having the faintest idea what I was doing, I soaked the Qld Maple before bending....

It was very hard to make it maintain it's shape when I got the curves I wanted, and I ended up with a little "wrinkle" in one of the waists. I strongly suspect all of this was due to it being too wet...

Here's a couple pics, one with, one without flash....

brunswick rose 002 (Small).JPG (93.72 KiB) Viewed 19176 times

brunswick rose 004 (Small).JPG (87.95 KiB) Viewed 19176 times

I have no idea what the consequences of this will be...

I'm really only looking for a guitar that plays OK for my first one, and to learn as much as possible about the entire process....

[Allen]

I've never used any softening agents. I know some guys who have a hell of a lot more experience than me use them on stubborn woods, and others with just a much experience won't touch them with a barge pole. As long as I'm not having difficulties, using them is not on the cards.

The "Old School" ways of soaking many woods I think stems from having to bend them on a hot pipe. Today with the silicone heat blanket and solid forms you can get away with a lot less water. There are quite a few of the uke guys using 2 blankets. One on each side because so many of the bends are every bit as tight as a venetian cutaway.

[P Bill]

If you read through Benedetto's book on arch top guitars he tells you to take them down to around the 1.8mm if memory serves me. Doesn't reinforce them after either as the area in the bend is stronger than that on the flats.

You're right. I mainly just look at the drawings after a skim thru the text.

[Bruce McC]

Hi John

I have used oxalic acid to remove green stains on blackwood sides, after bending in a side bender
using steel slats. It worked well for me with no apparent detrimental effects on the timber. I used
a saturated solution of oxalic acid and brushed it on liberally, over the whole surface area of both sides,
as it is a bleech and I wanted to avoid any patchiness or colour variation. Let it dry out then washed the
sides liberally with water. (One application was enough to remove the stains.)
I also wiped the sides with metho as I have been led to believe that this will help neutralise any acid residue.
If you don't remove all traces of acid from the timber you may get deposits of small white crystals of acid
appearing on the surface of the timber. The sides were left in a body mould to allow them to dry out
and stop springback.

I bought my oxalic acid from a local pool shop and I have also seen it in hardware shops that have sausage
sizzles on the weekends. It is considered to be a dangerous chemical and you should read the MDS sheet for
oxalic acid and follow the appropriate precautions when using it.

Rob may wish to add further comments on using oxalic acid.

Are you coming to the NFF this year?

[Bob Connor]

The main reason I ask is that in Kinkade's book, he recommends soaking rosewood before bending. Now, not having the faintest idea what I was doing, I soaked the Qld Maple before bending....

It was very hard to make it maintain it's shape when I got the curves I wanted, and I ended up with a little "wrinkle" in one of the waists. I strongly suspect all of this was due to it being too wet...

Here's a couple pics, one with, one without flash....

brunswick rose 002 (Small).JPG

brunswick rose 004 (Small).JPG

I have no idea what the consequences of this will be...

I'm really only looking for a guitar that plays OK for my first one, and to learn as much as possible about the entire process....

I suspect that wrinkle is because the wood was not pliable enough when you bent it.
ie
1. it wasn't hot enough or
2. the bend was done too quickly
or
3. the side was too thick.

Regards

[woodrat]

Hi John

I have used oxalic acid to remove green stains on blackwood sides, after bending in a side bender
using steel slats. It worked well for me with no apparent detrimental effects on the timber. I used
a saturated solution of oxalic acid and brushed it on liberally, over the whole surface area of both sides,
as it is a bleech and I wanted to avoid any patchiness or colour variation. Let it dry out then washed the
sides liberally with water. (One application was enough to remove the stains.)
I also wiped the sides with metho as I have been led to believe that this will help neutralise any acid residue.
If you don't remove all traces of acid from the timber you may get deposits of small white crystals of acid
appearing on the surface of the timber. The sides were left in a body mould to allow them to dry out
and stop springback.

I bought my oxalic acid from a local pool shop and I have also seen it in hardware shops that have sausage
sizzles on the weekends. It is considered to be a dangerous chemical and you should read the MDS sheet for
oxalic acid and follow the appropriate precautions when using it.

Rob may wish to add further comments on using oxalic acid.

Are you coming to the NFF this year?

Hi Bruce....Thanks for your experience with oxalic acid....I think vinegar would be the neutralising agent to use though....

and yes, I am coming to the National

[Nick]

My two cents (or 1.25 cents after tax):
The Blackwood I've bent, I've managed to sand out any staining but I use bugger all water for bending these days anyway. I bend over an Ibex style iron (aluminium body) & I've found that over time with each build, the amount of water I've applied has decreased to the extent that I just spray each side lightly so that if you held it vertically the water only just starts forming droplets but doesn't 'run' down the wood. Figured timbers get even less & I've managed to avoid any scorching by doing a bend in steps.

[Kamusur]

Good stuff gents and ty Allen.

Steve

[jeffhigh]

[Hi Bruce....Thanks for your experience with oxalic acid....I think vinegar would be the neutralising agent to use though....
)

Vinegar is also an acid, and hence will not neutralise oxalic acid. You would need to use an alkali.

[Lillian]

If you are looking for something to neutralize an acid, use baking soda.