Nouveau moyen de préparer la couche sensible des plaques destinées à recevoir les images photographiques / Lettre à M. Arago

A technical letter presents a refined method for preparing photosensitive metal plates, explaining how layered metallic iodides and thin deposits of mercury, gold and platinum produce galvanic effects that allow a thicker iodide coat and richer tonal gradations. It supplies practical reasoning, lists reagents and apparatus, and gives exact preparations and step-by-step operations for cleaning, polishing, bathing, heating, iodizing and fixing, with cautions about bromine exposure and the fragility of the gold layer. The account distinguishes a long, reusable preparatory sequence from a final iodizing step that should follow within about twelve hours.