Cone 10 experiment

Here is a bowl fired to cone 10. I glazed the interior with a cone 6 clear and then cone 10 jeff's red. The outside was glazed in a cone 10 black. My idea was to cause some movement of the jeff's red glaze. My instructor thinks that some black was "pulled" off the rim and that's what caused the blue color. I'm going to do some more experimenting and see what happens.