This is the plus 100 mesh particulate from 50 grams of two different ball clays. Most of the particles are carbon, they will burn out and possibly cause glaze defects. If any of them are metallic, they will produce fired specks.
Specking on Ceramic Ware
Specking, or speckling, can be both a fault or feature in fired ceramic ware - caused or produced by metal-bearing contaminants to metallic additives