A sepia-toned photograph taken in in 1895 Aerial view of downtown Houston 1977 A digitally sepia-toned image taken in 2007
In , toning is a method of changing the color of photographs. In , it is a chemical process carried out on silver-based . This darkroom process cannot be performed with a color photograph. The effects of this process can be emulated with software in . There is debate whether a toned black-and-white photograph should be considered to still be black-and-white, as simply being monochromatic is not a sufficient condition for an image to count as black-and-white.
Most toners work by replacing the metallic in the with a silver compound, such as (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 shades visible in a print without reducing the contrast. 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 those including iron and copper, can make the print less stable. Many chemical toners are highly toxic, some even containing chemicals that are . It is therefore extremely important that the chemicals be used in a well ventilated area, and and face protection should be worn when handling them.
Selenium toning is a popular archival toning process, converting metallic silver to . In a diluted toning solution, selenium toning gives a red-brown tone, while a strong solution gives a purple-brown tone. The change in color depends upon the chemical make-up of the photographic emulsion being toned. papers change dramatically, whilst pure papers change little. Fibre-based papers are more responsive to selenium toning.
Selenium toning may not produce prints quite as stable as or toning. Recently, doubts have surfaced as to the effectiveness of selenium toner in ensuring print longevity.
Sepia toning is a specialized treatment to give a photographic print a warmer tone and to enhance its archival qualities. The silver in the print is converted to a compound, which is much more resistant to the effects of environmental pollutants such as atmospheric sulfur compounds. is at least 50% more stable than silver.
There are three types of sepia toner in modern use;
Except for polysulfide toners, sepia toning is done in three stages. First the print is soaked in a bleach to re-convert the metallic silver to . The print is washed to remove excess potassium ferricyanide, and 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.
Fred Judge FRPS made extensive use of sepia toning for postcards produced by the British picture postcards manufacturer .
Metal replacement toners replace the metallic silver, through a series of chemical reactions, with a salt of a . Some metals, such as platinum or , can protect the image. Others, such as (blue toner) or (red toner), may reduce the life of the image.
Metal-replacement toning with gold alone results in a blue-black tone. It is often combined with a sepia toner to produce a more attractive orange-red tone. The archival Gold Protective Solution (GP-1) formula uses a 1% gold chloride stock solution with sodium or potassium thiocyanate. It is sometimes used to split tone photographs previously toned in selenium for artistic purposes.
Dye toners replace the metallic silver with a . The image will have a reduced lifetime compared with an ordinary silver print.
Toning can be simulated digitally, either in-camera or in . The in-camera effect, as well as beginner tutorials given for software like or , use a simple tint. More sophisticated tends to implement sepia tones using the feature. Simpler photo-editing software usually has an option to sepia-tone an image in one step.
The examples below show a digital color photograph, a black-and-white version and a sepia-toned version.
The following are examples of the three types using film:
Chemical toning (formulas and technique):