Siegen, Ludwig von (lŏtˈvĭkh fən zēˈgən) [key], c.1609–1680, German engraver, b. Holland, educated in Germany. He is said to have invented (c.1640) the mezzotint process of engraving. Among his seven known plates are portraits of Amalia Elisabeth of Hesse and of William II, prince of Orange, and his wife, Mary. His new method of engraving, long a secret, was revealed to Prince Rupert of the Palatinate in 1654. Through him it was communicated to the English engravers. A collection of Siegen's work is in the British Museum.