Using stonewares it is easy to get pretty sloppy in the studio because a particle of iron or cobalt in a glaze or body is no big deal. But on a ice white, translucent, transparent-glazed piece it is a really big deal. These specks are particles of cobalt that were trapped in my 80 mesh glaze screen from previous use. I use a soft brush to coax the glaze through the screen faster, but even that was enough to dislodge some of the cobalt particles. The lesson: I need a dedicated glaze screen for use with this transparent glaze, it gets used for nothing else.
Specking is a fault in fired ceramic ware where speckles of ion bearing contaminants are visible and mar the appearance of the surface.
Standard porcelains used by potters and for the production of sanitary and table ware have surprisingly similar recipes. But their plasticities vary widely.
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