Thanks, guys--I'll try these suggestions. Worst case I might end up
looking for a new piece of sheet metal!

Joe

Joe Landau wrote in
:

I have a piece of sheet steel that looks to be tinned, about 8x7",
that is part of a 70 year old box I'm refinishing. It has acquired
some stresses, and won't lie flat, though it will spring into several
stable states, like, boing!. How can I get it to relax, so I can
rebuild the box without stresses?