Enlarging paper is paper which has been covered in a light sensitive emulsion for the purpose of developing photographs. Using enlarging paper is an important step in film photography, as it turns film into prints. Some people call enlarging paper photo paper or developing paper, referring to various other steps in the developing process. Many photography supply companies sell a range of enlarging papers.
The base of enlarging paper is, of course, paper, which is covered in an emulsion of a photo-reactive metal such as silver or palladium suspended in gelatin. Specialty papers may have additional layers as well, intended to perform various roles in the developing and archival process. When exposed to light, the photo-sensitive emulsion reacts, and the image can be brought out with the use of developing chemicals.
The emulsion on enlarging paper is designed to be sensitive to a particular wavelength of light, often blue/green, allowing photographers to use “safelighting” in a color such as red or orange. This low light level allows photographers to see what they are doing as they work in the darkroom. Specialty enlarging paper may be treated for different wavelengths.
Different types of enlarging paper are used for different styles of photography. Black and white photography requires one type, for example, while developing color photographs involves a different sort of enlarging paper. Most enlarging paper is designed to work with a negative to positive process, meaning that the film is a reversed negative of the final image and the enlarging paper will yield a positive when it is exposed.
Some enlarging paper is made with a resin layer, which can be used to make a photograph matte or glossy. Resin is also easier to work with than fiber paper, another type of enlarging paper, since it takes less time to process. Fiber paper absorbs photographic chemicals, meaning that it needs to be carefully handled and thoroughly washed before it is dried. This enlarging paper is more stable in the long term, and is often used for professional prints.
There are a number of ways to expose enlarging paper. Most people use the paper in the context of a darkroom, which is a controlled light environment. Photographers can use a darkroom tool called an enlarger to project an image into enlarging paper, or they can make a contact print, by pressing a negative or object directly against the enlarging paper and then exposing it. After exposure, the enlarging paper is developed, stopped, fixed, and washed to produce an enduring photographic print.