A compound of aluminum silicate known as mullite (Al6Si2O13) is the secret component of the alchemists' crucibles used almost half a millennium ago across Europe and known to be among the most thermal and chemically resistant objects in the alchemical den. Researchers at University College London and Cardiff University have used petrographic, chemical, and X-ray diffraction analysis to demonstrate that crucible makers in Hesse, Germany, used an advanced material only properly characterized in the last century. UCL archeologist Marcos Martinón-Torres explains: "Our analysis of fifty Hessian and non-Hessian crucibles revealed the secret component." The crucible makers were not aware of mullite specifically, but they knew that firing kaolinitic clay at 1100 Celsius would make crucibles tough enough for alchemical reactions.
Crucible chemistry snookered no more