The reduction was fairly heavy and this piece went to cone 11. The tiny iron stone concretion particles melted vigorously and flowed. This is why clean firing results requires 200 mesh materials!
Particle Size Distribution
Knowing the distribution of particle sizes in a ceramic material is often very important in assessing its function and suitability for an application.
Specking is a fault in fired ceramic ware where speckles of ion bearing contaminants are visible and mar the appearance of the surface.