bitumen of Judea

In 1925, L. R Clerc wrote: “the only technique used at the start of photoengraving, Syrian bitumen, called judean (asphalt), has gradually been abandoned in favour of bichromate albumin. This later technique obtains the same results but takes much less time”. Bitumen does not seem to have been used in photomechanical processes after 1930.

The screening of printing plates engraved with photographs was one of the major advances to have been made among the various improvements to the asphalt technique invented by Niépce as applied to plate-making for printing. Thick varnish was no longer necessary to reproduce varying shades of darkness. Instead, the denseness of points did the work. This meant that the varnish could be very thin and consequently exposure time was reduced. By working on selecting different qualities of bitumen, on their purification, and on their enrichment with sulphur, their light sensitivity was considerably increased, resulting in the kind of rapid treatment needed for industrial production. This was not true of Niépce’s heliograph.

All this research gave birth to photoengraving and Niépce is undoubtedly its inventor.

note 

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.