Historically considered the premier, treasured, hand-coated emulsion among photographers, platinum and the closely related palladium printing processes are two of the tonally richest—that is, they can render nine shades plus D-max—and most permanent emulsions available. Depending on the paper and processing procedures used, the more expensive platinum can yield cool velvety blacks, while palladium renders warmer blacks and sepia browns. Palladium chloride is slightly toxic upon skin contact and inhalation, so handle it with care and use a skin barrier cream. Platinum chloride is moderately toxic by skin contact and may cause allergic reactions. Potassium dichromate, which can be added to hydrochloric acid to increase sensitivity, is moderately toxic upon skin contact and ingestion, but highly toxic upon inhalation and affects marine animals when flushed into bodies of water. Gold chloride solution can be added to palladium sensitizer, a few drops at a time, to warm the color or even turn it pink.