Editing Photographic developer (section)

{{Short description|Chemical(s) which convert a latent image on photographic film to a visible image}}
{{more footnotes|date=March 2019}}
[[File:Boîte avec 5 doses de révélateur universel en poudre au génol-hydroquinone de la société Guilleminot 02.jpg|thumb|Developer powder using genol-hydroquinone.]]
In the [[Photographic processing|processing of photographic films]], plates or papers, the '''photographic developer''' (or just '''developer''') is one or more chemicals that convert the [[latent image]] to a visible image. Developing agents achieve this conversion by [[Redox|reducing]] the [[silver halide]]s, which are pale-colored, into [[silver]] metal, which is black when in the form of fine particles.<ref name="Ullmann">Karlheinz Keller et al. ''Photography'' in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a20_001}}.</ref> The conversion occurs within the gelatine matrix. The special feature of photography is that the developer acts more quickly on those particles of silver halide that have been exposed to light. When left in developer, all the silver halides will eventually be reduced and turn black. Generally, the longer a developer is allowed to work, the darker the image.