Chromogenic Prints

Manufacturing

The image formation principle depends on a reaction between chemicals during development in which the dyes are formed. The process is based on the trichromatic subtractive colour system: the photographic support is made of three layers of gelatin, each containing one of the three dyes, cyan, magenta, or yellow on a baryta paper, a resin coated paper (RC) or a plastic film. The azomethine dyes that will shape the image are formed during the development, proportionally to the exposure to light. Laboratory processing is highly constrained (successive passages in baths at strictly constant temperatures, total darkness), which has limited the production of these photographs to machine processing.

Identification

Colour negatives and slides produced from the 1940s onwards are all chromogenic photographs. When examined under magnification, the paper prints display a characteristic grain structure that makes them easily distinguishable from photographs using additive synthesis systems (Autochrome, Dufaycolor, etc.). They often have the manufacturer’s name printed on the reverse. They have white margins and may have various finishes (matt, rough or glossy). Their soft colour range is distinctive and sets them apart from Cibachrome®, which are more saturated and glossy, or dye transfer, which has a much wider colour range and margins where the trichromatic colour addition is visible.

Deterioration

Even if the Kodachrome® has a very good resistance to light, it is an exception, the chromogens dyes being very sensitive to pollutants, the light and to storage conditions (temperature, humidity). Each dye has its own stability and the deterioration of the image often manifests itself by the fading of certain dyes and the appearance of a dominant colour.

Glossary