So the high heat was at the most likely shocked this pot the other piece must have been better protected. The restart could also have caused unequal heating. My best guess initially is that heat at the start would crack the pot not pot lid the surface. However i can produce the surface
with a propane torch on un-fired pottery. So a very hot flame licked the side of this pot as the fire was lit. Most likely in that first five minutes.
Result # 2
This pot is not cracked at all even with the pot lid surface wow! It has a great ringing sound when struck to it indicating that we had enough heat to do the work we wanted.
Result # 3 the area that is pot lidded has same coloration therefore the same carbon up take. This would also indicate that it occurredearlier in the firing and during a time of reduction.
Results#4 the lip is the most delicate part of the pot and should have been placed down.
Result# 5 shell particles look simular in quantity to the photo provided earlier in this post