In photogravure on copperplate, etching is commonly done by immersing the plate in several solutions of ferric chloride of different concentration. As the pigmented gelatin is thicker where the image tone is higher, the trick is to allow the ferric chloride to penetrate beginning by the thin gelatin in the shadow areas and progressively do …
Photographer & Printmaker / A Hybrid Place About Early Photography and Digital Imaging
Carles Mitjà - ASIS/FRPS 