Chemical Toning
Most toners work by replacing the metallic silver in the emulsion with a silver compound, such as silver sulfide (Ag2S) in the case of sepia toning. The compound may be more stable than metallic silver and may also have a different color or tone. Different toning processes give different colors to the final print. In some cases, the printer may choose to tone some parts of a print more than others.
Toner also can increase the range of visible shades visible in a print without reducing the contrast. Selenium toning is especially effective in this regard. Some toning processes can improve the chemical stability of the print, increasing its potential longevity. Other toning processes, such as iron and copper toners, can make the print less stable. Many chemical toners are highly toxic. It is extremely important that the chemicals be used in a well ventilated area. Rubber gloves and face protection should be worn when handling them. Some toners contain chemicals that are carcinogenic.
Read more about this topic: Photographic Print Toning
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