Black spots on Oak

[D._Frederick]

While gluing up oak, I end up with black spots from the reaction with the glue and the iron clamps. On sold wood I just sand them out, but with veneer that is only 1/32 inch thick that don't work.

Does bleaching work and what kind of bleach?

[beenthere]

Maybe best is don't let the steel touch the oak.

Use some thin pieces of plastic, or scrap veneer, or other material under the steel of the clamps.

You also can try some samples of black stain from the clamps, and see if bleach will work. I don't believe it will be effective enough.

[ohsoloco]

I usually use wax paper in between the clamps and wood to prevent staining.  Don't know how you would remove the stain though  :-\

[CHARLIE]

Buy a can of that plastic that you can dip handles and stuff in to give them a rubber type coating. Then dip the tips of your clamps in it.   

[LeeB]

Somebody correct me, but I think oxalic acid will take the stains out.

[SwampDonkey]

I believe your right LeeB. I've never heard of it before, but did a quick Google and seems like a lot of hits about stain removal. I know a natural source of oxalic acid is wood sorrel, but never heard of it's use on stain. I also know that it can cause your speech some trouble if enough is ingested from those sorrel garnished salads. ;)

[okie]

does Galvanized metal still cause the black stain?

[ohsoloco]

Buy a can of that plastic that you can dip handles and stuff in to give them a rubber type coating. Then dip the tips of your clamps in it.   

Charlie, it's not so much the tips of the clamps that cause the problems (at least in my experience, anyway), but the actual iron pipe.  The glue from the joint seeps out and then comes in contact with the pipe...this is where the black/blue staining occurs. 

[LeeB]

Galvinized will help but the clamps don't bite as good and tend to slide on the galvinized.

[Dodgy Loner]

Oxalic acid will work from what I've read. I use galvanized pipe clamps and have had no problems with slipping. If your clamps slip, it's the clamps' fault, not the pipes!

[isawlogs]

 It is the tannin in the oak that , when in contact with steel/iron will oxydise and cause the blue stain. Stainless steel will prevent/solve this . Any of you that have a sawmill will have noticed when sawing oak, helmlock, butternut also, that any part of that wood that comes in contact with bunks or clamps that are not covered with stainless steel will get this reaction.

[SwampDonkey]

Butternut will stain quick for sure.  But it sands off a lot quicker than oak.

[fiddle1]

oxalic acid works -----its like a salt ----sometimes called wood bleach-----water it down first.
little bit goes along way its best to use dust mask when you use it

[woodsteach]

Yep use the oxy acid.  Daub a little on a swab and wipe it on the stain and usually it goes away!

[JimTwoSticks]

Iron-Tannic stain can be a pain (how poetic) :

This document is a good summary of what it is and how to fix it/prevent it
http://www.fpl.fs.fed.us/documnts/finlines/willi02c.pdf