This is more like etymology of the day than word of the day. It’s an excuse to link to this: Did You Know: Sepia Toning is Named After the Common Cuttlefish:
Sepia is a dark brown-grey color, named after the rich brown pigment derived from the ink sac of the common cuttlefish Sepia. The word sepia is the Latinized form of the Greek σηπία, sēpía, cuttlefish.
Sepia toning is a specialized treatment to give a black-and-white photographic print a warmer tone and to enhance its archival qualities. Chemicals are used to convert the metallic silver in the print to a sulfide compound, which is much more resistant to the effects of environmental pollutants such as atmospheric sulfur compounds. Silver sulfide is at least 50% more stable than silver.
There are three types of sepia toner in modern use;
- Sodium sulfide toners – the traditional ‘rotten egg‘ toner;
- Thiourea (or ‘thiocarbamide’) toners – these are odorless and the tone can be varied according to the chemical mixture;
- Polysulfide or ‘direct’ toners – these do not require a bleaching stage.
Except for polysulfide toners, sepia toning is done in three stages. First the print is soaked in a potassium ferricyanide bleach to re-convert the metallic silver to silver halide. The print is washed to remove excess potassium ferricyanide then immersed into a bath of toner, which converts the silver halides to silver sulfide.
Incomplete bleaching creates a multi-toned image with sepia highlights and gray mid-tones and shadows. This is called split toning. The untoned silver in the print can be treated with a different toner, such as gold or selenium.
Black and white is monochrome. Sepia is another form of monochrome, using brown as the shadow color, just as cyanotype uses blue for the shadow color. When the highlight color is something other than white it’s called split toning.
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