Photographic print toning

In photography, toning is a photographic process carried out on silver-based (black-and-white) photographic prints to change their colour. Some toning processes can improve the chemical stability of the print and allow it to last longer. Other toning processes can make the print "less" stable.

Many early prints that exist today were toned with sepia toner.

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 colour or tone. Different toning processes give different colours 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 tonality of a print. This increases the range of visible shades without reducing contrast. Selenium toning is especially strong in this regard.

Many toners are highly toxic. It is extremely important that the chemicals are used in a well ventilated area. Rubber gloves and face protection should be worn when handling them. Some toners are carcinogens.

Metal replacement toning

Metal replacement toners replace the metallic silver, through a series of chemical reactions, with a ferrocyanide salt of a transition metal. Some metals, such as platinum or gold can protect the image. Others, such as iron ("blue" toner) or copper ("red" toner) may reduce the lifetime 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.

elenium toning

Selenium toning is the most popular of the archival toning processes, converting metallic silver to silver selenide. In a diluted toning solution, selenium toning gives a red-brown tone, while a strong solution gives a purple-brown tone. The change in colour depends upon the chemical make-up of the photographic emulsion being toned. Chlorobromide papers change dramatically, whilst pure bromide papers change little. Fibre-based papers are more responsive to selenium toning. [cite web | url=http://www.ilfordphoto.com/aboutus/page.asp?n=135 | title=Selenium Toning | publisher=Ilford Photo | accessdate=2007-05-11]

Selenium toning may not produce prints quite as stable as sepia or gold toning. However, its appearance is much more subdued than sepia and it is cheaper than gold. Selenium toning also increases the tonal range available in the paper.

Different printers use somewhat different methods of selenium toning, but most often a fixed (and perhaps rinsed) print is placed in selenium toner solution and then rinsed, treated with hypo clearing agent, washed, and hardened.

Recently, doubts have surfaced as to the effectiveness of selenium toner in ensuring print longevity. [cite web | url=http://www.silverprint.co.uk/News05_9.htm | title=Silverprint News May 07 | date=May 2007 | accessdate=2007-05-11]

Sepia toning

The term 'sepia' comes from the name of an artists' pigment made from the Sepia cuttlefish, found in the English Channel, Sepia officinalis, the Common Cuttlefish.

In sepia toning, chemicals 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. This is why many old photographs are sepia toned—those are the ones that have survived until today.Fact|date=April 2008

There are three types of sepia toner in modern use;
# Sodium sulfide toners - the traditional 'rotten egg' toner;
# Thiourea (or 'thiocarbamide') toners - these are odourless 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 grey 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. [cite web | url=http://www.xeromag.com/fvresrc.html#Anchor3 | title=Photographers' Resources: Toning | publisher=Xero magazine | accessdate=2007-05-11]

Dye toning

Dye toners replace the metallic silver with a dye. The image will have a reduced lifetime compared with an ordinary silver print.

Digital "toning"

Toning can be simulated digitally, either in-camera or as a later post-process.

The in-camera effect, as well as beginner tutorials given for software like Photoshop or The GIMP, use a simple tint which is usually a poor imitation. More sophisticated software tends to implement sepia tones using the duotone feature. See Sepia tone.

See also

* Cyanotype
* Platinotype

References

External links

* [http://www.ilfordphoto.com/applications/page.asp?n=97 Ilford: Toning prints]
* [http://www.ephotozine.com/techniques/viewtechnique.cfm?recid=105 Sepia toning] in a developing tray.