ABSTRACT
Ethylenediaminetetraacetic acid (EDTA) is a polycarboxylic amino acid widely used to chelate to iron and calcium ions to help remove them from the paper. Disodium EDTA is acidic, which is needed in the first bath after development for kallitypes to prevent iron hydrolysis, which leads to print yellowing in highlights sometimes years after processing. Unlike the Vandyke brown and argyrotype processes, the kallitype process is a developing out process that requires a developer to create the final silver image on paper after UV exposure. Vandyke brown is a printing-out process that is developed in distilled water, so no developer is required. When using drops of dichromate in the sensitizer, the first water development tray will contain minute amounts of sensitizer.
