Problems steam bending white oak

My steam bending chamber (3-inch steel pipe x 60 inches long with 1500 watt electric heater in one end) 3/4 full of water, quickly comes up to the pressure switch set point of 10 psi, and has worked ok for some years, usually bending hickory for Windsor chair backs. Now, when I try to use it on white oak, the wood has a nasty black color. Why? One theory has something to do with the tannic acid I believe is present in the oak, but I'm no chemist. Is there a reaction between the steel pipe and the oak? Any comments are welcome. Dave
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Tannic acid present in the oak is reacting with the iron in the steel.

Me neither, but from what I understand some people actually use vinegar with iron soaked in it to "ebonize" their oak.

Try googling a bit on "ebonize or ebonizing, oak, vinegar, tannic acid, etc..."
JP
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wrote:

In past times, Japanese women used this same preparation to blacken their teeth for cosmetic reasons.
(And before we feel too smug, European women of the same period were using white lead as a skin foundation)

You bet there is !

Plastic gas main pipe for oak. Less risk of burning yourself when handling it too. I've also never needed to pressurise a steam chamber.
--
Smert' spamionam

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David Anderson asks:

It's not a theory, it's a fact. You need another steam bending chamber of a material other than steel or iron.
Charlie Self "The test and the use of man's education is that he finds pleasure in the exercise of his mind." Jacques Barzun
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