first rocket stove – observations (found glass)

So I disassembled my first rocket stove yesterday and found a few interesting things:

First, a layer of steel from the inside of the drum had come loose and mostly blocked the bell exhaust… which explains the terrible draft and smoke.
However the more interesting one is… I made glass.

The lower part of the inside of the riser (made from fine sawdust and clay) cracked and turned into a glass. I am not really sure what is going on here…
Then I found that the bricks of the tunnel near the riser also turned into glass.
Has anyone else seen this?

Hi Sebastian,   I have not made a sawdust and clay riser as you have, (rather a perlite and clay riser) but at the bottom mine has done something similar to this. Apparently the hottest part of the rocket stove is right around the end of the burn tunnel and a small way up the heat riser. The extreme heat from extended fires could cause the material to melt somewhat and produce these fissures. Essentially, your clay has turned into pottery.

Any properly functioning RMH will get hot enough to turn a clay lining into pottery; yours has gotten even hotter and vitrified the clay, which literally means "made glassy".

Thank you Glenn and Gerry for pointing this out. How I have to try melting some more clay…