Actually, obsidian is a working material that you don't need to heat treat. I suspect what you got on had is just bad obsidian (well, for knapping, anyway)...remember, obsidian is a glass, made in volcanoes, and the problem might not be water at all, but the gasous composition of your material...the Obisidian Spirit did not create all obsidian to be equal.
Speaking for myself, I prefer to use obsidian (from
www.neolithics.com) or glass. When I get flint, it's already heat treated, which is a slow process of bringing the heat up slooowly, and bringing it down slooowly. Otherwise, you get...gravel. For much more info than you could ever think of using, consult my friends at...
http://groups.yahoo.com/group/TheTarp Caveman Bob