Georges Rouault, French. Born 1871. Grimacing Man from Flowers of Evil. Aquatint.
The top narrow rectangle is an enlarged cross-section showing particles of resin on a plate surface.
1. Stopped out* before biting
2. One-minute bite - then stopped out.
3. 4 minute bite- then stopped out.
4. 16 minute bite, then stopped out.
Intaglio process. A tonal medium which permits 'grainlike' values in the print ranging from silvery grey to intense black. A porous ground of resin or other substances in applied to the plate, heated, then etched a number of times to produce the required values. (Jules Heller)
* Stopping out: Preventing certain lines or areas of a plate from biting, by brushing on an acid-proof material.