Traditional chemical toning is the process of intensifying or changing the tone of a photographic print after processing. Solutions called toners are used to produce various effects. There are a number of possible reasons for toning prints. The principal ones are:
For aesthetic effect or the creation of mood - for many years photographers have been using toners to change the appearance and improve the appeal of their pictures. Toning is a useful aid to creating atmosphere and establishing mood. Naturally warm subjects such as portraits and sunsets often benefit from the addition of warm brown or red tones, whereas cold subjects such as snowscapes are likely to benefit from the addition of blue tones;
- to achieve a different overall print colour - the use of dilute toning baths can produce prints with subtly different overall colours;
- to increase maximum print density - some toners, such as the blue and selenium types, increase density, while others such as sulphide and dye toners, reduce density;
- to provide a print with additional protection - some toners convert or coat silver images in a way that provides greater protection against the ravages of time and external contaminants; and
- as a test of adequate fixing - prints that are not fully fixed will exhibit staining when transferred to a toning bath, so test-strips can be assessed in this way./li>
The main types of toner are:
- Indirect Sulphide Toners - these use a two-stage bleach and redevelop process to convert a silver image, partially or completely, to brown silver sulphide. The bleach is usually ferricyanide bromide which converts the image to silver bromide. The redevelopment solution can be sodium sulphide but this has an unpleasant odour and has been replaced in many cases by other odourless toners. Prints toned in indirect sulphides generally have lower density and contrast than untoned prints.
- Direct Sulphide Toners - these are single-solution toners that act directly on silver images to change it partially or completely to silver sulphide. These toners work slowly at room temperature and have the advantage that toning can be stopped when the desired result is achieved. Prints toned in direct sulphide toners have similar contrast and density to untoned prints.
- Selenium Toners - these produce prints with higher density and contrast than untoned prints. The single-solution toners partially covert silver images to silver selenide. The degree of toning may be controlled by changing the dilution of the toner and the toning time.
- Gold Toners - these are usually single-solution toners that shift a print towards blues and blacks. However, they are often used in conjunction with a sepia toner to produce an attractive orange or red. Gold toners generally produce prints of similar contrast and density to untoned prints.
- Metal Replacement Toners - blue toners produce prints with higher contrast and density than untoned prints. Red toners produce prints with lower density and contrast than untoned prints. Metal replacement toners convert silver images to the ferricyanide salt of one of several possible transition metals. Vivid colours can be produced.
- Dye Toners - in this case the silver image is replaced with a dye image.