Nicéphore Niépce’s photogravure copy of an engraving by Isaac Briot is a key milestone in the invention of photography and of photomechanical reproduction. It dates to 1826—a dozen years before the world at large learned of the existence of photography. By using a varnished (transparent) copy of Briot’s engraving as a negative and a light-sensitive etching asphaltum called bitumen of Judea, Niépce was able to transform a sheet of pewter into an etching plate that could be inked and printed to yield a rough reproduction of the original engraving.