Editing Photographic processing (section)

===Black and white negative processing===

[[File:Photographic processing.jpg|thumb|center|upright=3.0|Black and white negative processing is the chemical means by which photographic film and paper is treated after photographic exposure to produce a negative or positive image. Photographic processing transforms the latent image into a visible image, makes this permanent and renders it insensitive to light.]]

# The film may be soaked in water to swell the [[gelatin]] layer, facilitating the action of the subsequent chemical treatments.
# The [[photographic developer|developer]] converts the latent image to macroscopic particles of metallic [[silver]].<ref>Wall, 1890, p. 30–63</ref>
# A [[stop bath]],{{efn|In modern automatic processing machines, the stop bath is replaced by mechanical squeegee or pinching rollers. These treatments remove much of the carried-over alkaline developer, and the acid, when used, neutralizes the alkalinity to reduce the contamination of the fixing bath with the developer.}} typically a dilute solution of [[acetic acid]] or [[citric acid]], halts the action of the developer. A rinse with clean [[water]] may be substituted.
# The [[photographic fixer|fixer]] makes the image permanent and light-resistant by dissolving remaining [[silver halide]]. A common fixer is ''hypo'', specifically [[ammonium thiosulfate]].<ref>Wall, 1890, p. 88–89</ref>
# Washing in clean water removes any remaining fixer. Residual fixer can corrode the silver image, leading to discolouration, staining and fading.<ref>{{Cite web |title=Photochem |url=http://sites.tech.uh.edu/digitalmedia/materials/3351/PHOTCHEM.pdf |archive-url=https://web.archive.org/web/20180124135711/http://sites.tech.uh.edu/digitalmedia/materials/3351/PHOTCHEM.pdf |archive-date=24 January 2018 |website=University of Houston College of Technology}}</ref>
The washing time can be reduced and the fixer more completely removed if a [[hypo clear|hypo clearing agent]] is used after the fixer.
# Film may be rinsed in a dilute solution of a [[non-ionic]] [[wetting agent]] to assist uniform drying, which eliminates drying marks caused by [[hard water]]. (In very hard water areas, a pre-rinse in [[distilled water]] may be required – otherwise the final rinse wetting agent can cause residual ionic [[calcium]] on the film to drop out of solution, causing spotting on the negative.)
# Film is then dried in a dust-free environment, cut and placed into protective sleeves.
Once the film is processed, it is then referred to as a ''negative''.

The negative may now be [[Photographic printing|printed]]; the negative is placed in an [[enlarger]] and projected onto a sheet of photographic paper. Many different techniques can be used during the enlargement process. Two examples of enlargement techniques are [[dodging and burning]].

Alternatively (or as well), the negative may be [[film scanner|scanned]] for [[digital printing]] or web viewing after adjustment, retouching, and/or [[Photograph manipulation|manipulation]].

From a chemical standpoint, conventional black and white negative film is processed by a developer that reduces silver halide to silver metal, exposed silver halide is reduced faster than unexposed silver halide, which leaves a silver metal image. It is then fixed by converting all remaining silver halide into a soluble silver complex, which is then washed away with water.<ref name="shinsaku"/> An example of a black and white developer is Kodak D-76 which has bis(4-hydroxy-N-methylanilinium) sulfate with hydroquinone and sodium sulfite.

In graphic art film, also called lithographic film which is a special type of black and white film used for converting images into [[halftone]] images for offset printing, a developer containing methol-hydroquinone and sulfite stabilizers may be used. Exposed silver halide oxidizes the hydroquinone, which then oxidizes a nucleating agent in the film, which is attacked by a hydroxide ion and converts it via hydrolysis into a nucleating agent for silver metal, which it then forms on unexposed silver halide, creating a silver image. The film is then fixed by converting all remaining silver halide into soluble silver complexes.<ref name="shinsaku"/>