potter's earth

Go," said he, "to the Queen's prison; hand the gaoler this lump of potter's earth, and tell him to place it in the death-chamber of Chrysis the courtesan.

The mineral products comprise lignite, limestone, gypsum, alum and potter’s earth; barley and rye are the usual cereals; fruits and vegetables are abundant; and considerable quantities of hemp, flax, hops and tobacco are raised.

All the workers do is to pick it up as it comes in the reservoir, to pile it, and, when the heap is of a certain size, to cover it with a thin coating of potter’s earth. 

She and they were both clay, to be sure, but she was of the finest porcelain clay and they of the coarsest potter's earth.

If you will have pure carbon, carbuncle, or diamond, to make the brain transparent, the trunk and organs shall be so much the grosser: instead of porcelain, they are potter's earth, clay, or mud.