80 pounds of dry obsidian

[caveman2533]

Nice, It has something to do with internal stress in the rock I think similar to when glass isn't annealed correctly. I think a higher temp could even be used.

[Zuma]

Agreed
Hope to see you with a few flakes in tow.
Thanks again

[Zuma]

Well, I got a different hammerstone (sandstone). The first one I used was quartzite.
My first spall removal with it was ok but the spall came off in two parts.
The larger piece is ok but has more curve than I would like.

Things went down hill from there. I tried a hit where the core was
 not as long in the direction I was taking the spall.
 Even so the spall terminated  premature of what I had hoped.
(right side of first flake)
 The next try was back to the right of the second spall.
I really beefed up the platform and gave It a hardy blow.
The platform just collapsed.
It's back to the drawing board for now.
Between the first go rod and the second I at least have some pretty
good material for the oven.
Zuma

[caveman2533]

To hard of a hammer stone will split  spalls

[Zuma]

Well, Steve,
I would'nt argue with you because both Quartzite (first hammer)
and my next best hammer (Sandstone) are pretty hard.
I think I will find a ladies bowling ball and give it a go.
Better hammer /platform contact I hope.
Zuma

[Zuma]

Well, Steve
I took the latest spalls and cooked
them longer and hotter. About 10 hrs overall
and a 3 hr soak. Not really much difference
for the extra energy.
The upside-- nothing blew
Zuma

[Zuma]

Here is the results of a piece I knapped
 of the latest batch cooked.
Not to pretty but it came from a really square
hunk. It was pleasing to knap. Just percussion.
Zuma