Rick, I've tried the different soak times everybody recomends. If the rock is real rough, like low grade chert, I'll cook it about 3 hours around 300dgs to dry out moisture. Then crank it up and let it go all night. If it is Coral or Jasper or high grade Chert, that is real dense, I crank the dial to 450 or 500 and turn it off in the morning when I go to work. When I get home it is usually cool. Just make sure your pieces are not too thick or you will have to do it again once you thin it.