Dry plates had been tried before: and had no effect silver nitrate with a binder of albumen - derived from egg white, and widely used in printing-out paper in the nineteenth century - had been coated on glass; but these proved to be too insensitive for camera use. Gelatin had also been suggested by photo-theorist and color pioneer Thomas Sutton, and the substance would also have been known to Maddox - himself an eminent microscope practitioner - through its use as a holding/preserving base used in microscope slides.