Made in Germany, Anno 1600
A good idea will prevail when its time has come. Even without being understood, as ceramics from the Middle Ages prove: They owe their excellent properties to the same material mix that is used today in aircraft wings, catalytic converters and modern refractory materials.
Being a university professor far away from the Oxford research site, the Honorable Robert Plot found, is sometimes a real disadvantage. How on earth are you supposed to work properly as an alchemist and chemist, get to the bottom of the inner substance and the very nature of things - if you don't have the necessary tools? When native craftsmen are too clumsy, England's own wares inferior, and the only acceptable quality must be imported at great expense? Ironically from the continent, from Hesse?
During Plot's lifetime in the 17th century, but even before that in the Middle Ages, the dependence on a certain piece of quality Made in Germany was extremely annoying on the island. For centuries, Hessian regions have been export world champions for this special technical product - the almost indestructible crucible that allowed alchemists, minters and metallurgists to do their trade. As late as 1755, after literally millions of German goods had already had to be imported to the island, the Royal Society of Arts called on local manufacturers to finally learn how to produce similarly high-quality laboratory equipment using local materials. The reason was obvious: the funds for importing were eating away at the reserves.
All efforts to copy the Hessian quality of crucible production remained unsuccessful attempts from the late Middle Ages to the no longer early modern period: Crucible works from outside the Hessian region broke more easily and cracked at lower temperatures. And so, from the British Isles to Spain to Scandinavia or the New World, crucibles from central Germany remained unrivaled for a long time because they were unrivaled in quality. What, not only Robert Plot asked himself in 1677, is behind the "secret of the Hessian goods" jealously guarded by the producers?
Archaeologist Marcos Martinón-Torres of University College London and his colleagues were looking for answers a good three centuries later. Using an electron microscope and X-ray diffraction analysis, they scrutinized almost fifty old original crucibles in order to track down the superior material properties of Hessian provenance.
Crucibles from Hesse, according to their first insight after petrographic and chemical analyses, were apparently made according to a typical standard recipe that was always followed. A clay that was very lean in the mineral kaolinite was always hardened with almost pure quartz sand, formed on the potter's wheel and fired. This alone contributed to the desired material properties of the product: the resulting crucibles had favorable aluminum to alkali and alkaline earth element ratios, which contributed to the tolerance to high temperatures; the up to forty percent high proportion of non-deformable inclusions made of rounded quartz granules also increase breaking strength and thermal stability.
However, a very similar mineral mix can also be found in competing products from the Hessian melting pot. Their real unique selling point lies in the inner structure of the ingredients, which only forms at the firing temperature of 1100 to 1200 degrees Celsius, which was unusually high for Europe in the late Middle Ages. Martinón-Torres believe that this alone led to the secret of Hessian ceramic success: synthetic mullite. The aluminum silicate (Al6Si2O13) is formed from kaolinite at high temperature – and interlocked in the pottery, needle-like embedded in a matrix of quartz and other clay minerals, to form an almost unassailable ceramic felt. Much like the medieval crucible producers, materials scientists today also benefit from mullites: The silicates are indispensable components of extremely hard-wearing modern high-performance ceramics, which are used in civil engineering, fire protection and aircraft construction.
Without knowing mullite, the crucible producers used its properties for centuries - understandably, they guarded their recipe for as long as a state secret. To the chagrin of crucible-dependent alchemists like Robert Plot from Oxford - or his older colleague Thomas Norton from Bristol, who complained about the lack of engineering spirit of his compatriots: Good crucibles, he wrote in 1477, were made "in no country on English soil".
