Weigh it at regular intervals until it stops loosing weight.
It's then reasonably safe to start shaping into something resembling any blanks you should want.
At this stage try putting a sample in a sealed plastic bag and see if moisture collects on the inner surface.
If it's small enough you can give it, in its bag, a quick burst (seconds not minutes) in the microwave at a low level to see how much moisture is still in there.