In most colour processes, colours dyes are formed during the chemical treatment. Impurities inevitably appear during chromogenic processing. This is not the case with Cibachrome. Colour dyes are incorporated into the sensitive layers of the material during manufacturing. The main advantage of this technique is that the purity and the light stability of these dyes can be strictly monitored. Control of these elements give Cibachrome its unique qualities. Once exposed, the sheet of paper is processed; the final colour rendering depends on the amount of dyes destroyed during processing. Yellow dyes, for example, are destroyed to produce the blue parts of the image. A main feature of a Cibachrome print is its outstanding colours, with an estimated permanence of more than 300 years (Kodak study 1989, Sciences et vie magazine). This make a favourite amongst artists, exhibitors and collectors. One can therefore wonder why chromogenic papers have not been abandoned and replaced by Silver Dye Bleach. The answer lies more ib historical than in technical reasons.

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Although the 150th anniversary of the birth of photography was celebrated in 1989, colour photography as we know it and use it today is a much more recent invention. It took a whole century to reach the era of modern colour photography. Ducos du Hauron's and Charles Cros's research -superimposition of three colour prints, 1867 - led to the Freres Lumiere's, then to the introduction of the first commercial process, the Autochrome; the work of hunderds of researchers was necessary before the launch of Kodachrome in 1935; this shows the amazing path it took for an invention to reach its present technological stage. These discoveries are all based on the principles of additive synthesis of blue, green and red or of the substractive synthetis of their complementary colours : cyan (blue-green), magenta (blue-red) and yellow, to re-create the colour spectrum. The final results is obtained by the superimposition of three films or by exposing three sensitive layers coated on film or paper.

The idea of the bleaching of a dye in contact with a silver image comes frome the last century. Although the first findings are attributed to the English scientist Herschel (1880), the experiments of the French Vallot (1885) and the German chemists Liesegang (1897) and Shinzel (1905), the patent of the Danish Christensen (1918) have largely contributed to a wider knowledge of the process. But it is the Hungarian Bela Gaspar who was the final winner in the development of the process (1929). Industrial production, however, was delayed by technological problems. In the meantime, the chromogenic technology was making great progress. The first negative colour films appeared in 1936. Kodachrome and Agfacolor were perfect for diffusion in both the amateur market and in the professional fields of photography and movie makers. Colour printing vas about to come up. From then on, all industrial efforts were concentrated on this sole issue. It took almost 35 years for the Silver Dye Bleach partisans to develop industrial manufacturing : the Cibachrome, manufactured and distributed bye Ilford Anitec.

The structure of the emulsion is identical in all colour processes. Silver halide crystals are incoporated into three blue, green and red sensitive layers. In chromogenic processes, yellow, magenta and cyan dyes are formed with the help of colour couplers incorporated into the layers; the dyes are formed in proportion to the exposure received (blue, green and red light respectively) to restitute the colour of the original. In the case of Cibachrome, dyes of azo type (yellow, magenta and cyan) are already present in the emulsion in a saturated form; they are destroyed during processing, in proportion to the quality of complementary light received (blue, green and red light respectively), that is in proportion to the amount of silver formed in these three layers.

After Canon, Nikon, Kodak, Polaroid and Agfa, it's Ilford Imaging Switzerland's turn to bid adieu to film photography. Unable to compete with digital photography, the 125-year-old business is shedding half its staff and its range of traditional products to avoid bankruptcy, marking the end of an era.

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