"Jim Weisgram" wrote in message
...
On Sun, 8 Jul 2012 16:47:59 -0700 (PDT), Sonny
wrote:

I would suspect the panel is air dried wood (best/easiest carved when
still some greenness to it), not kiln dried.

The back side seems to be unfinished. Is this correct? If so, then I
would try dampening the back side (and leaving the damp cloths laying
on the panel) and see if the panel straightens, on its own, a little,
after a period of a few hours of dampness only. Place some moderate
dead weights in position to straighten the panel. If there is a hint
of straightening, after a few hours, then I would reapply some
dampness and gently shoot some *heat onto the panel while applying
some dead weight pressure to straighten the panel more..... Possibly
rigging up a dead weight press, first, to assist while warming/heating
the dampened panel. If the wood is air dried, it should respond to
some dampness and/or some heat with pressure, similar to steaming wood
for bending. This may be easier and safer than trying to cut relief
kerfs (as a last resort?).

*Note: Do not apply high heat with this procedure. Good warmth,
~150°, not too hot, at all. Also, when applying heat, don't apply too
much initial dead weight pressure. Place small pressure and gradually
increase, if need be.... but first, see if the panel responds to just
dampening the back side, with no heat assistance.

Sonny

Wouldn't adding moisture on the back cause those fibers to swell,
increasing the cupping?

Yes.
Art