Developing photograph (image 2 of 2). Black and white print appearing while being washed in developer in a darkroom. When a photograph is taken, a negative is made of the image (lighter areas appear dark and vice- versa). The negative is then exposed onto photographic paper, which is coated in silver- halide ions. White light displaces the ions. The paper is then washed with developer, which is a reducing agent. It converts the silver ions to silver metal, forming the dark areas of a black and white photograph. Only red light can be used in a darkroom when developing photographs because white light would distort or destroy the photographic image.