Historically, it was extremely difficult to produce a clear, deep red colour in glass as the colour was derived from a precipitate of gold. But In 1679 the alchemist and glass-maker Johann Kunckel (1630-1703), working for the Elector of Brandenburg near Potsdam, appears to have been the first to achieve consistent results in sizeable batches. The use of gold to colour glass may seem strange today, but it should be remembered that both gold and ruby were believed to be empowered with magical properties - the latter bringing strength and health, and safeguarding its owner against sorcery. Kunckel was secretive about the exact processes involved in making ruby glass. Nevertheless, by the end of the century the secret of its manufacture had spread to other parts of the Holy Roman Empire; and during the late 17th and early 18th centuries glass with a deep ruby tint was produced in Dresden and Bohemia, and in Munich and Freising in southern Germany.