concave it will be and thank you all for the help. I really would have stopped on the percussion when I made the post but was not sure which way to go. I think I can thin better on the next one now that I understand how the bopper responds to the small platform. I really had to take small bits from the platform and with conviction at the sametime. Boy it takes a lot of practice to learn flint knapping. You guys really are a talented group. I will post the finished piece in a day or so.
