How to straighten picture frame moldings

Hi everyone, I recently purchased a half a dozen 8’ softwood and a couple hardwood picture frame moldings. I generally check them over pretty carefully. But this time I was in a hurray and they looked great so I didn’t check them very well. Latter on when I went to use them I realized that each piece had its own unique twist, bow or bend. Not that noticeable until I lay them on the bench. My question is, can anyone give me there techniques for straightening light weight wood like moldings? I used clamps on a piece of maple and left it for a week or so and it did straighten out some but not to the perfection that we like for picture frames. I live about an hour from the store where I purchased them or I would have taken them back. I look forward to your reply. JohnT, Stettler, Alberta, CA

-- jft