I have been steam bending cherry and finishing with polymerized tung oil. On one piece iron stains appeard after bending and drying. These were treated with an oxalic acid solution successfully. In this case apparently I neglected to wash out the acid well afterwards and now after applying the polymerized tung oil and having the surface age for about 3 months in strong light, pink stains have appeared. I have stripped the finish with Citristrip. Does anyone know any chemistry that might remove these stains.
Thanks, John.
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Is it that the stained areas have become lighter, or they just haven't darkened like the rest of the wood? If they're just "undarkened," you can neutralize the acid with dilute ammonia, and the lighter areas will eventually catch up with the rest, although there will probably always be some noticeable difference. The ammonia will actually take the wood in the other direction somewhat, causing it to darken much like it would on exposure to sunlight, so you need to keep a close eye on what you're doing.
(It's more common to use lye--sodium hydroxide--to darken cherry, but ammonia has the advantage in that it is somewhat self-neutralizing, since the residual ammonia evaporates. In either case, the resulting color really isn't quite the same as you get with long-term exposure to light; it has a slightly greener cast.)
-Steve
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