I've now put more than a few of these platters through the kiln; I've learnt something about my kiln as a result.
My bottom shelf sits flat on the bottom of the kiln, no props underneath. I've learnt that a platter with such a wide flat base suffers from thermal shock as a result. Obviously the heat is retained in the base and walls of the kiln longer than in the atmosphere, as a result the base of the platter is hotter than the wall of the platter and as the wall of the platter changes from α-quartz to β-quartz the base has not changed at the same time. The result is thermal shock during quarts inversion. (α-quartz separates from β-quartz) This is interesting stuff, until you find a large platter at the bottom of the kiln with a massive crack through it after days of waiting and anticipating as it slowly goes through its firing.
This little platter is my favourite, so I'm keeping it. It has pride of place at the moment and receives coin donations every time I come home from shopping.
http://en.wikipedia.org/wiki/Quartz_inversion
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