Could these bentonite particles cause specking in a porcelain?

Sunday 24th July 2011

The stated particle size of a material and fired appearance can both be misleading. For example, these are Volclay 325 bentonite particles fired to cone 8 oxidation. They are from a water washed sieve analysis test, the oversize particles from a 325 mesh screen (left) make up 2% of the total and 1% are from the 200 mesh screen (right). Although the 325 particles appear ominously dark, individually they are likely to small to produce apparent fired specks in a porcelain. However 200 mesh sizes can produce visible fired specks, but that fraction of oversize does not have nearly as high iron or flux content. Still, the finer darker particles could agglomerate, it might be better to use a cleaner bentonite to plasticize a porcelain.

Pages that reference this post in the Digitalfire Reference Database:

Bentonite, Volclay Bentonite, SIEV Sieve Analysis 35-325 Wet, Particle Size Distribution, Specking

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of