4. Edouard Denis Baldus (ca. 1813-1890)

Baldus used a classic technique, first making an asphalt image on copper from a positive proof that turned into a negative on the metal (a).




L. Figuier tells us in 1869: "The picture is formed by a veil that is so thin and delicate that part of it would quickly disappear when the plate was immersed in liquid. To give it more suitable solidity and resistance, it was left for two days in diffused light." Baldus then put the plate in an electrolytic bath and, depending on whether he connected the plate to the negative or to the positive pole, he obtained either a reproduction in copper-deposit relief (b) or an intaglio engraving on the parts of the plate that were attacked (c).


In this manner, he could obtain either an engraving similar to an etching destined for copperplate printing or a copper plate engraving that could be included directly in the printing plates.





5. Berchtold, Egloffstein

A decisive step in photoengraving was the use of halftone screens that broke up continuous shading into networks of points. This led to stabilizing the ink so that it was consistently placed on the paper. As of 1853, the Englishman Talbot spoke of using "a crepe or black gauze veil" placed between the photosensitive plate and the image that was to be produced which broke the engraving’up into a multitude of tiny squares. In 1859, Berchtold exposed his negatives on a metal plate smeared with asphalt. He then exposed the plate a second time across a piece of glass on which he had traced a series of fine parallel lines and a third time after having rotated the glass plate. After dissolving unexposed asphalt, he obtained an image composed of squares, lozenges, etc.

In 1861, Baron von Egloffstein used Berchtold's method in the heliographic institution he had set up in Philadelphia. He was, in particular, responsible for engraving federal government bank notes.