Obsidian Tumbling

I'm on my 4th batch of obsidian slabs (I'm planning a windchime project) and have had great results. The flow lines show really well in the sunlight, which is why I thought of windchimes.

My formula: I mix the slabs (edges rounded off with the trim saw) with cubes. I cut cubes of obsidian to keep my saw blade clean, so they are really just a by-product of saw usage.
In my 3# barrel, I can fit 6-8 slabs, and a dozen or so cubes, depending on the size. I cut cubes 1/4" to 1/2". Then add about 1/2" of ceramic beads. I've tried plastic beads in different combinations with obsidian, and HATED my ceramic beads at first. But the ceramic beads just work really well with obsidian.
I run for 2 weeks in 69/90, re-charging after a week (or so). Then 10 days in 120/220. Be sure to check the barrel now and then - obsidian is gassy, and may need a gas-relief tablet or two. I then run for just 5 days in 500 pre-polish, then burnish really well (24 hours this time) with borax. Then add polish - tin oxide seems to work the best. I get a glossy, drop-dead finish in about 5 days.
I read through a lot of recipes on this board and other places on the net and tried Karo syrup, sugar in the mix....all kinds of combinations - and messes! This one just seems to come out consistantly beautiful.

Turq