Avoiding Iron Stain when Steam-Bending Red Oak
Oak and other high-tannin woods react with water and iron to create black staining. Here's how to prevent it. December 8, 2006
I have a proposed job that requires steam bending red oak. My client is concerned that the oak will develop black blotches. In previous jobs involving steaming red oak I haven't had problems. Was I just lucky or should I be concerned?
(Furniture Making Forum)
From contributor D:
You have to keep the wet wood away from all iron. The ferrites in the iron/steel will react with the tannins in the oak and cause an ebonizing stain. It’s great when you want ebonized, terrible when you don't want it. Use a plastic steam chamber, stainless boiling pots and parts, and clean water. Then do a trial run to insure the results.
From Gene Wengert, forum technical advisor:
Iron tannate stain can be removed instantly with oxalic acid.
From contributor B:
Contributor D is correct. It’s not so much the wetness that will cause the spots but the iron. Have you ever noticed if you get a drop of blood on oak that it will turn black when it dries? That’s because of the iron that is present in your blood. Although I will say I have experienced dark blotches as a result of the wood getting wet, I’m talking a bottle of water being spilled on them and not just a run through the steam box.