Aluminium quickly develops a thin oxydized layer when it comes into contact with air and displays a silver gray surface colour. This robust layer possesses first class corrosion resistant qualities. According to Plinius, aluminium was discovered during the reign of Tiberius (14-37 A.D.). A metal worker offered it as a gift to the emperor and was beheaded as a reward - because Tiberius feared that the new metal would undermine the value of gold and silver. That's the story.