Broken crucible base found in Chahak
Modern-day chromium-alloyed stainless steel used in the production of quality tools was being made by ancient Persians a millennia ago, centuries earlier than previous estimates.
The discovery, published in the Journal of Archaeological Science, resulted from archaeological finds at the 11th century site of Chahak in Iran demonstrating that metalworkers of the time were intentionally adding chromium to their crucible charge. A crucible steel flint striker found dating from the same period contains chromium, suggesting it was made in Chahak.
Chahak is described in a number of historical manuscripts dating from the 12th to 19th century as a once famous steel production centre, and is the only known archaeological site within Iran's borders with evidence of crucible steel making. Researchers from University College London were particularly intrigued by the manuscript 'al-Jamahir fi Marifah al-Jawahir' (A Compendium to Know the Gems) written by the Persian polymath Abu-Rayhan Biruni which included the only known crucible steel making recipe. This recipe recorded a mysterious ingredient ‘rusakhtaj’ which they identified as chromite.
These findings are significant given that material scientists, historians and archaeologists have long considered that chromium steel was a 20th century innovation.
Sources: University College London