Wet plate collodion (originating from 1850s) can be made on glass as positive or negative image, and on metal as a positive. The collodion photographer has 10 to 15 minutes time span for pouring iodized collodion on the plate, sensitizing it in silver nitrate solution, exposing in a camera, and processing the plate. The plate must not dry during the process – if it does, no image will result. When shooting outdoors, a portable darkroom is needed for processing the plates.