Photographic paper
The initial light exposure is carefully controlled to produce a grayscale image on the paper with appropriate contrast and gradation.
A range of emulsions are also available that differ in their light sensitivity, colour response and the warmth of the final image.
After the early days of photography, papers have been manufactured on a large scale with improved consistency and greater light sensitivity.
In black-and-white papers, the emulsion is normally sensitised to blue and green light, but is insensitive to wavelengths longer than 600 nm in order to facilitate handling under red or orange safelighting.
[2] In chromogenic colour papers, the emulsion layers are sensitive to red, green and blue light, respectively producing cyan, magenta and yellow dye during processing.
[3] Most fiber-based papers include a clear hardened gelatin layer above the emulsion which protects it from physical damage, especially during processing.
[2] Fiber-based papers are generally chosen as a medium for high-quality prints for exhibition, display and archiving purposes.
The brightening occurs because barium sulfate is in the form of a fine precipitate that scatters light back through the silver image layer.
After adding enough yellow filtration to make a neutral, the blue sensitivity of the slow cyan layer is "lost".
[2] Popular in the past, chloride papers are nowadays unusual; a single manufacturer produces this material.
[8] These insensitive papers are suitable for contact printing, and yield warm toned images by development.
[3] Papers with pure silver bromide emulsions are sensitive and produce neutral black or 'cold' blue-black image tones.
VC papers permit the selection of a wide range of contrast grades, in the case of the brand leader between 00 and 5.
Upon exposure to blue light, all emulsions act in an additive manner to produce a high contrast image.
[citation needed] Panchromatic black-and-white photographic printing papers are sensitive to all wavelengths of visible light.
They were designed for the printing of full-tone black-and-white images from colour negatives; this is not possible with conventional orthochromatic papers.
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,[14] 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.
