In the context of photography, Sepia is a brown toner used for printing photographs.
Originally, sepia was used in chemical photographic printing. More recently, sepia also refers to the brown toned digital photographs which imitate the older chemical format.
In the days of chemical processing black and white pictures were processed using metallic silver as an ingredient of a chemical emulsion. In the sepia process metallic silver was replaced by the alternative, silver sulphide. Silver sulphide toner is a more stable than the metallic silver emulsions. As a result the brown toned sepia photographs last longer making them ideal for archiving and preservation.
Sepia, the colour, gets its name from the rich brown coloured ink derived from the cuttlefish Sepia. The ink from Sepia has been used as an art and writing medium for centuries. The chemical development process gets its name from the similar rich brown colour to the sepia ink.
Sepia has a flexible tonal range. It can create rich brown and white photographic prints. It is also suitable to be printed as a range of shades of brown at different toner density and pattern on the print medium.
Sepia is a safe emulsion commonly used in photographic printing. Other brown toned chemical toners may not be safe to handle. When handling lots of old films wear protective gloves to prevent direct skin contact.
Today, sepia chemical processing is a three stage chemical process which has a number of variations. Various compounds can be used to have induce different toning capabilities. Sepia can also be mixed with alternative toners resulting in the creation multi-toning effects, mid-tones and shadow forms allowing multiple tonal forms in the final print.
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See also: Simple ideas about sepia effects for more information.