Calling the process heliography (“sun drawing”), Niépce succeeded from 1822 onward in copying oiled engravings onto lithographic stone, glass, and zinc and from 1826 onto pewter plates. 
<Context ref.>Heliography (from photography, history of) -- Encyclopædia Britannica. [En línia]. [Consulta: 1 juny 2006]. Disponible a: <http://www.britannica.com/eb/article-252842>