Ball milling
An hour in a ball mill does less than I thought for this clay. This is all of the oversize on a 35-200# PSD test of a clay body slurry of a 50-gram sample (thus the +200 mesh material). The oversize on the right was measured after 1 hour in our ball mill (porcelain jar). That hour only reduced the total +200 oversize from 7g to 3g.
