Up to the Middle Ages, seven metals were only known and used by man. These were gold, silver, copper, iron, lead, tin, and mercury. During the Middle Ages the metalloids arsenic, antimony, and bismuth were isolated as well as zinc that was imported from the East. In the Eighteenth century mineral specimens were continuously supplied and analyzed which resulted in the discovery of about a dozen new metals. With the discovery of electric current at the beginning of the nineteenth century the alkali metals were isolated and these were responsible for the isolation of new metals that were not possible to isolate before, such as aluminum, zirconium, titanium, etc. Once aluminum became available it was used to liberate other metals from their compounds. The industrial revolution in England started by replacing charcoal by coke followed by the Age of Steel while the discovery of X-rays towards the end of the century resulted in many more discoveries that changed our world in the twentieth century. English text available in Encyclopedia of Materials: Science & Technology, Elsevier 2001, pp. 5537–5541