Plumbago Crucibles: Fire Clay, Coke and Graphite, Ure 1839

Crucibles must stand sudden heating and cooling without cracking. Andrew Ure (1839) gives the best as pure fire clay with ground old crucibles, black lead (graphite) and some coke: a Berlin mix of 8 parts clay and cement, 5 of coke and 4 of graphite stood 23 meltings of 76 lb of iron each. Mix it like a pottery body, press it into crucibles, dry them slowly and fire them. The picture: used graphite crucibles.