1819-1823 — Invention of photoengraving
After the Gaïacum resin, Niépce used another resin, consisting of mineral: asphalt or bitumen of Judea. He demonstrated that under light action this resin became non-soluble with his usual solvent.
From 1822 on, he succeeded in reproducing drawings put in contact with bitumen coated bases (glass plates, calcareous stones, then copper or tin plates). Afterwards, he used the aqua fortis process to etch the images made with acid, which were then printed on paper. This process was to remain for quite a while the base of photoengraving used to print photos and graphical documents.
Principle and technique
In order to reproduce drawings, around 1822-1823, Niépce conceived what we now call the contact print. He explains clearly how he applied varnish to the verso of an etching to make the paper translucid, and once dry, he applied this etching directly in contact with the copper or tin plate coated with bitumen varnish. He exposed the lot in full daylight during three to four hours, then rinced the plate in lavender oil diluted with white kerosene. The bitumen that had been protected from the effect of light under the lines of the drawing then dissolved and let appear the raw metal. On the other hand, the light transmitted through the translucid paper had made the bitumen non-soluble and remained on the plate after the lavender oil rinse. The bitumen image was the drawing’s negative: the back is colored in the dark bitumen brown and the lines are represented by the raw metal.
Then, Niépce invented a process that would allow to get the drawing etched in the metal. It was by means of the well known and simple principle of aqua fortis. The plate carrying the bitumen of Judea is dipped in an acid bath that bites the metal where it is not protected, meaning the places corresponding to the lines of the drawing. Because the bitumen varnish is acid resistant, the acid can penetrate down to the metal. Once the lines are etched in the plate, Niépce eliminated the bitumen varnish from the metal base to keep only the etched drawing on it.
The first successful results of this method can be dated to 1822, as far as contact reproductions are concerned, because this year Niépce made a copy the portrait of Pope Pius VII on a glass plate. This was not yet an acid etched engraving. The earliest attempts of etching in 1823 are not on metal but on lithographic stones. A Dijon-based printer produced paper prints from those stones. Thus, Niépce got the proof that his process — by means of contact reproduction — allowed for the multiplication of originals through printing.
In 1825, he etched his images on copper, from 1826 onwards on tin.
The acid process is perfectly appropriate to reproductions of line drawings, in which gradations are represented by hatchings. In the case of images with continuous tones, these are reproduced by various thicknesses of bitumen that acid etching cannot render, as the acid solution cannot permeate the varnish. Niépce understood this phenomenon and worked continuously to reproduce etchings. Many museums throughout the world preserve metal plates etched by the inventor with this process.
The Niépce Museum owns ten of those metal plates on which Nicéphore reproduced engravings. Other Niépce etched metal plates are preserved at “La Societe française de Photographie”, at “The Royal Photographic Society” or in Janine Niépce’s collection. Yet, after his numerous failures to etch continuous tones images obtained with a camera obscura, Niépce gradually gave up acid etching and stopped completely after July 1827.
