Only knapped on new years eve but the material is awesome. Oddly that slab of obsidian broke in half on the first strike of the bopper. It must have had a minute freeze fracture or something. One of the halves did the same thing. VERY unusual for a piece that thick. I'm showing a friend of mine how to knap and he got one of the glass preforms skinned on one side. When it warms up again I will get back after it. Thank you so much! I have some points picked out to send you Pat.