Medieval manufacturers used 'high-tech' chemical to toughen crucibles

Using petrographic, chemical and X-ray diffraction analysis, Dr Martinón-Torres and colleagues from Cardiff University established that a highly resistent alumininium silicate called mullite - today used in building and catalytic converters - was behind the renowned durability of 15th-century crucibles made in Hesse, Germany. The crucible makers produced the chemical by using clay rich in aluminium silicate and then firing the mixing vessels at 1,100 degrees.Hessian crucibles have been found in archaeological sites in Scandinavia, Central Europe, Spain, Portugal, colonial America and millions were imported into Britain alone. At the time, they were the gold standard in what was a key part of the alchemist's kit and saw off several poorer imitations.

• Links:
• 'Nature' paper: 'Mullite and the mystery of the Hessian wares'
• Dr Marcos Martinón-Torres
• Read the full press release