Here's a strange result:
Used some old pieces of angle iron as grate bars in wood fire (cone 11+)
When opening the kiln there was some strange blue green stuff in the ashes left behind;
Unfortunately the stuff got on pots too:
It seemed to react especially terribly with an iron celadon (Mark's tenmoku with 2% iron)
but also made ugly stuff on shino and even unglazed wares.
Wondering if any one has seen problems from rusty metal in a kiln before:
The iron came from an old railroad bridge (1940's maybe)
The bars were rusty on the surface but still dense and heavy.
After the firing it was flaking in big chunks.
Could the problem be from just the iron?
I am thinking that some other impurity in the metal vaporized.
Perhaps the iron was poorly smelted in the first place and was giving off something like whatever is in the blue slag you find around old iron processing furnaces ?