Photographic paper is a paper coated with a light-sensitive chemical formula, like photographic film, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion. The most common chemistry was based on Silver halide (the focus of this page) but other alternatives have also been used.
The print image is traditionally produced by interposing a photographic negative between the light source and the paper, either by direct contact with a large negative (forming a contact print) or by projecting the shadow of the negative onto the paper (producing an enlargement). The initial light exposure is carefully controlled to produce a gray scale image on the paper with appropriate contrast and gradation. Photographic paper may also be exposed to light using digital printers such as the LightJet, with a camera (to produce a photographic negative), by scanning a modulated light source over the paper, or by placing objects upon it (to produce a photogram).
Despite the introduction of digital photography, photographic papers are still sold commercially. Photographic papers are manufactured in numerous standard sizes, paper weights and surface finishes. A range of emulsions are also available that differ in their light sensitivity, colour response and the warmth of the final image. Color papers are also available for making colour images.
The longevity of any photographic print media will depend upon the processing, display and storage conditions of the print.
Fixing must convert all non-image silver into soluble silver compounds
Fixing must convert all non-image silver into soluble silver compounds that can be removed by washing with water. Washing must remove these compounds and all residual fixing chemicals from the emulsion and paper base. A hypo-clearing solution, also referred to as Hypo Clearing Agent, HCA, or a washing aid, and which can consist of a 2% solution of sodium sulfite, can be used to shorten the effective washing time by displacing the thiosulfate fixer, and the byproducts of the process of fixation, that are bound to paper fibers.
Toners are sometimes used to convert the metallic silver into more stable compounds. Commonly used archival toners are: selenium, gold and Toners are sometimes used to convert the metallic silver into more stable compounds. Commonly used archival toners are: selenium, gold and sulfide.
Prints on fiber-based papers that have been properly fixed and washed should last at least fifty years without fading. Some alternative non-silver processes – such as platinum prints – employ metals that are, if processed correctly, inherently more stable than gelatin-silver prints.
For colour images, Ilfochrome is often used because of its clarity and the stability of the colour dyes.