The crucibles were made by firing kaolinitic clay at temperatures greater than 1100°C, forming mullite. Mullite is an aluminum silicate only described in the 20th century and is responsible for the excellent properties of the Hessian crucible.
Crucibles were formed by heating kaolinitic clay at temperatures greater than 1100°C, resulting in mullite. Mullite, an aluminum silicate first described in the 20th century, contributes to the superior properties of the Hessian crucible.