I have a vague recollection that the method Bernt Damm is looking for
involves letting the Duo-Art expression box spend the night in your
deep freezer (or out on the porch over a Great Plains winter night).
The subzero temperature makes the old glue very brittle (but not so
much the wood), so a well-aimed hammer blow may indeed shock the glue
joints into letting go.

If I had it to do over again (I used the putty knife method first time,
can be scary!), I'd combine the two: freeze the box and then use the
putty knife.  I didn't own a freezer back then!

Mike Knudsen