Funny how questions pop up all at the same time. So I steamed the laurel bow for about 3/4 of an hour, clamped it straight for about 18 hours over night and when I took it out of the clamps it was lovely and straight. Two hours later it had completely gone back to its old shape, so, did I not clamp it for long enough, or not steam it for long enough, or should I have used dry heat - I put it back in the clamps to finish drying as it was still damp when I un-clamped it, but I think I am going to have to try again.