I took a little break from official duties in the City to zip to Sausalito for an afternoon. I had reserved a space on the 2:30 tour of Heath Ceramics - their factory that has been there, a low, slate-blue one-storey that looked suspiciously like my grade school, since the 1950's. Edith Heath worked with an architect on the design - it's cool, a square designed around a central courtyard where she could eat lunch and bring glaze tests out into the light to see what they 'really' looked like.
Two kinds of clay come off the truck and enter the building at one corner of the square - a white & a 'manganese' clay. These are blunged & can be pumped over to the next room to be poured into molds for slip-casting, or can be filter-pressed and recovered as large mats of clay suitable for press-molding & jiggering. At least - this is what I remember from the tour...
These plaster molds last for a while - a few hundred castings maybe - then need to be replaced. Even the prototypes used to form them degrade eventually, and need to be compared to original works in the Heath archive - carefully measured - is the shoulder of that bottle supposed to come out a little farther, or is that good?