This is what started me looking more closely at what appeared to be ordinary rocks. Some of them turn out to be..... rocks. Others????? This is the rock I put in the fire place. The image showed up after it cooled.
As a ceramicist I have answers for this. The color of the pigment is close to that used by the Colonial potters in their blue salt slip. The pigment was covered by a patina. The fire burned off the patina and renewed the coloring under it.
If you look carefully, you can see that there are other symbols on it.
You can now understand why I sat and looked at it for an hour after I pulled it out of the ashes.
Edited by red clay - 09-Jun-2011 at 14:02