Plaster for molding
at left middle margin of folio 165r
When it is long to set and dry, it means that it is too fat and moist, which is what makes it shrink away from the fire and crack. [This is] where burrs come from. The one that comes from lean earth is better. You must not store your moulds made of fat plaster for a long time, because they resemble fat earth, which when drying, cracks. The best is to reheat them soon after they have been made and cast. Moulds made of good plaster can be stored a long time.
It is necessary to oil it well, because it is more difficult to separate the two halves of these moulds than when it is mixed.