Editing Photographic processing (section)

== Further processing ==
{{See also|photographic print toning}}
Black and white emulsions both negative and positive, may be further processed. The image silver may be reacted with elements such as [[selenium]] or [[sulfur|sulphur]] to increase image permanence and for [[aesthetics|aesthetic]] reasons. This process is known as [[Photographic print toning|toning]].

In selenium toning, the image silver is changed to [[silver selenide]]; in [[sepia tone|sepia toning]], the image is converted to [[silver sulphide]]. These chemicals are more resistant to atmospheric [[oxidizing agent|oxidising agents]] than silver.

If colour negative film is processed in conventional black and white developer, and fixed and then bleached with a bath containing [[hydrochloric acid]] and [[potassium dichromate]] solution, the resultant film, once exposed to light, can be redeveloped in colour developer to produce an unusual [[pastel]] colour effect.{{citation needed|date=January 2009}}