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Read more: “Nine lost treasures – and why science wants them back“

European Crusaders returned home with tales of Islamic warriors wielding blades that could slice through a floating handkerchief, bend 90 degrees and flex back with no damage. They called the metal Damascus steel. Despite centuries of advances in material science, exactly how the Islamic swordsmiths created it is still unknown.

European blacksmiths at the time knew the blades were forged from crucible steel – created by melting iron with plant matter – but were unable to replicate the sharpness, flexibility and distinctive wavy markings. The metal has intrigued researchers from Michael Faraday to material scientists in the present day.

at Iowa State University has shown that only , bearing trace elements such as vanadium, would yield the right surface pattern. And in 2006, researchers at , Germany, studied the swords with an electron microscope and discovered that their strength probably comes from made from a mineral called cementite. Similar structures give modern composite materials their strength. However, the exact recipe still remains a mystery.