‘Le Cardinal d'Amboise’, made by Joseph Nicéphore Niépce in France, 1826.
‘Le Cardinal d’Amboise’ is one of the earliest photomechanical plates in existence and was taken from the original engraving ‘Georges Cardinal d’Amboise, Grand Ministre d’Estat et Légat en France’ by Isaac Briot (1585-1670).
Niépce made the first photograph on a pewter plate in 1826 or 1827. He named his process Heliography.
The Heliographic process used Bitumen of Judea, here on pewter, which hardens when exposed to light. To create a negative, an engraving was varnished, placed over the plate and exposed to sunlight. The soluble unexposed bitumen was dissolved in an oil of lavender-kerosene mixture and the plate was etched in an acid bath. The exposed hardened bitumen acted as a resist, so that the acid etched only areas of unexposed metal. The resulting heliographic plate was used to make final prints on paper.