4th August 2013
In 1850, the French painter Jean-Baptiste-Camille Corot pioneered a technique known as Clichés-verre.
The earliest use of the photographic principle in the making of line blocks did not involve a camera but were based on hand-drawn negatives. In 1850, the French painter Jean-Baptiste-Camille Corot pioneered a technique known as Clichés-verre. It was a hand-process that meant creating a glass photographic negative. The glass was coated with an opaque white substance and lines were etched on with a needle. The lines became the only transparent part of the plate, just as with a glass negative. Drawn glass negatives of this type later became part of a genuine printing process, but Corot used them for ordinary photographic purposes, treating them in the darkroom as conventional negatives. A sheet of photographic paper was exposed through the glass, and on the developed print the drawing appeared as black lines against white. A tonal effect could be achieved by painting a white pigment on a glass plate. Where the paint was thick, no light would get through to the photographic paper that would therefore remain white; as the areas became thinner, allowing varying amounts of light through, so the areas of the photograph showed a range of tones. The same results could have been got by lines drawn on white paper, or painting a tonal image in white on black paper with each photographed for darkroom printing.