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Got a blanket and spring steel slats from John. Followed directions to a "T" and the following pics happened. It isn't burnt. It looks like it was died. Bent the lower bout at 220, upper bout around 270, max temp around 310 and cooled off to 230. Granted...this is just practice wood, but I really don't want this to happen to my good wood. Any advice?!?! Thanks.

Ken

I guess the first question is, how were you measuring the temperature?

That certainly looks as though it got a lot hotter than 310F. But you say it's not burned.

Was there residual oil on the steel that discolored at that temp?

Did you use 2 pieces of paper? I use stainless steel . The spring steel will stain so use alumin foil or be sure to use 2 pieces of paper.
Start over clean the spring steel with and sos pad then use a barrier, Usually paper is enough to avoid this problem. Also make sure you temp is on F not C. To me it appears your blueing on the slats is what got you. Useing alum foil will avoid this for sure. Some paper is higher in acid that others so I use butchers paper now .
Let me know how you make out
at least the bends look good

John...thanks! I used 2 sheets of brown kraft paper...the same stuff we use to cover the table with when we steam crabs. It only did that on the very bottom, so I also wonder if maybe I didn't let it get hot enough to cook the water out? The top (where the heat was applied) has absolutely no staining. I have 1 practice piece left, and I'll try the aluminum foil. And I agree...after the first fiasco...the bends came out great!

Also...I'm using a digital thermometer with a 4 or 5 inch probe and it's pretty accurate from my test measurements.

I'll let you all know how the next test goes...and then it's time to split open the sapele!

next time have paper on both sides. You need that barrier to keep the iron ions from going into the wood.