|Cibachrome (the Silver Dye Bleach Process)|
Unlike conventional colour negative/positive printing papers, where the coloured dyes making up the picture were generated by colour couplers in a colour developer, Cibachrome print materials were manufactured with the dyes already incorporated in the printing paper.
Cibachrome materials, or papers, were multi-layer products, each layer containing a dye of the opposite colour to the layers sensitivity.
The top layer was sensitive
to blue light and contained a yellow dye.
One problem for any Silver Dye Bleach materials was their extreme insensitivity to light. This is because each layer has effectively a complimentary colour filter coated on top of the sensitive emulsion of that layer. For example, the top layer, sensitive to blue light, has a yellow dye placed over the blue sensitive emulsion, the opposite colour of blue.
The later Cibachrome print materials were manufactured with an extra emulsion layer coated adjacent to each of the dye containing layers. These extra layers contained no dye, but were in contact with the dye containing layers and served to increase the speed of the print paper.
The first person to achieve any success with the Silver Dye Bleach process was the Hungarian chemist, Dr. Bela Gaspar. Based on the work of another researcher, Carl Schinzel, Dr. Gaspar invented a colour transparency material for use with motion picture animated advertising films in the early 1930s. The films were made using a very complicated method, by making three exposures of each frame through tri-colour filters on black and white motion picture film. This produced a separate negative record of the red, green, and blue components of the picture. Because Dr. Gaspers material was a positive to positive printing material, each frame had to be printed again onto the black and white motion picture positive film to produce a transparency of each of the red, green, and blue records. Finally the black and white transparencies were printed through their corresponding tri-colour filters, a red record black and white transparency was printed through a tri-colour red filter (and so on) onto Dr. Gaspars colour Dye Bleach material to produce a colour motion picture film.
If Gaspars material had been made in large sheet film sizes, it could have been used to make duplicate transparencies, possibly from Autochrome, Dufaycolor, or other additive reseau transparencies. (Kodachrome 35mm film was first marketed in 1936). This was never done, but by 1945 a printing material known as Gaspar Opaque, similar to a reversal colour printing paper, was being made and sold in America for photographers to make their own colour prints from transparencies.
Another material, maybe an improved version, appeared in 1953. This later material was known as Gasparcolor DP (Direct Positive). It was obtainable in the USA, was similar to Cibachrome, and processed in much the same way. It was balanced for enlarger lamps (3200°K), and had to be handled in total darkness or under a safelight suitable for panchromatic black and white films (Wratten Series 3, or 5, or Ilford GB 908). It was said that with a brightness level of 10 foot candles, prints from average transparencies could be made with exposure times of 30 to 60 seconds. There was even a recommended filter pack for trial exposures given with each batch of Gasparcolor DP, possibly similar to the Grundzahl figures stamped on each packet or box of Agfacolor paper.
A stop-bath in step 2 was optional. If used, 30ccs of glacial acetic acid in 1 litre of water would have been a suitable formula.
A dozen sheets of 8 inch x 10 inch
Gasparcolor DP could be processed in 2 US gallons
of Developer or Dye Bleach. 2 US gallons
of Silver Bleach served to process twice this amount of print
In the early 1950s, no printing or processing machines were obtainable or sold in the UK for mass production printing of transparencies onto a print material. Ilford designed and made their own equipment, both printers and processors, for their colour print service. Instead of printing onto a multi-layer colour coupler type of paper, such as Anscocolor Printon, Ilford chose to employ a Silver Dye Bleach material. It was known as Ilford Colour Print Material.
Because of the extremely low light sensitivity of Silver Dye Bleach materials, the printing machines were equipped with 2¼ kilowatt Xenon arc lamps to make the printing exposures and thus achieve a reasonable print production rate of over 1,000 prints per hour.
The printing paper, or Silver Dye Bleach material, was allegedly made by Ilford Ltd, but was only for use in their laboratories for their print service. It was never sold on the open market, much in the same way as Eastman Kodaks Kodacolor paper.
In 1963 Ciba AG, Switzerland, approached Ilford with a buy-out offer. The Ciba group comprised (i) Ciba AG, Ciba Photochemie AG (formerly Tellko AG, research laboratory near Fribourg) a manufacturer of sensitised photographic materials, (ii) Lumière SA France (near Lyons, acquired by Ciba in 1962) also a manufacturer of sensitised materials & of colour film (in the 1950s), and (iii) Gretag GmbH (Germany) a designer and constructor of equipment and instruments for use in the photographic industry.
There was no take-over by Ciba until 1969 but there began commercial co-operation between Ciba and Ilford to develop Ciba's dye-bleach print material for making prints directly from colour transparencies. Originally called Cilchrome ('Cil' derived from the names Ciba, Ilford and Lumière) the eventual product name reverted to Cibachrome (1969 in the UK).
A processing procedure for Cilchrome was published in the British Journal of Photography for 19th June 1964, by E.Ch. Gehret. It was also reproduced in the British Journal of Photography Annual for 1965 and some following annuals. The chemical formulae, given in the annuals, were worked out by E.Ch. Gehret. It is not an exact procedure, the material was still at the research and development stage at the time the processing procedure was published. It is based on some of the patents taken out by Ciba Photochemie.
Silver Dye Bleach Materials work
The respective layer records the red, green and blue coloured image of the transparency, plus mixed colours, being recorded in two or, in the case of white, in all three layers.
After exposure, the material is developed in a black and white developer, fairly similar to one which might be used to develop black and white printing paper. This produces a negative silver image in each layer corresponding to a black and white negative of the red, green and blue components of the transparency.
For example, the image in the middle layer is a black and white negative of anything green in the transparency, or any colour which is partially green. A cyan colour, green/blue, would be recorded partly in the green layer and partly in the blue layer.
The next step is the Dye Bleach bath. The removes the coloured dye from the developed black and white negative image only, and leaves any dye not affected by the black and white developer. It works in the exposed parts of the red, green and blue images only. The remaining dye makes up the positive image to give a colour print of the transparency.
As the material still contains the unwanted exposed and unexposed silver halide, two more processing steps are necessary. In the next step i.e. the Silver Bleach step, the exposed metallic silver, formed by the black and white developer, has to be converted into silver halide which will be made soluble in the fixer.
The final chemical step is a Fixing Bath, which converts all the silver halides in the material, exposed and unexposed, to a soluble silver, which can then be washed out the print to leave only the dyes. The negative image is effectively removed from the Cilchrome (Cibachrome) print, the negative unwanted dye is bleached out in the Dye Bleach, and the exposed silver halide of the negative image is removed in the Silver Bleach and Fixer.
This is an outline of the earlier processing procedure. Later processes combined the Dye Bleach and Silver Bleach into one processing step. Earlier processes contained additional fixing baths as well as a separate Dye Bleach and Silver Bleach.
Sharpness and Dye Stability in Silver Dye Bleach Materials
Unfortunately, there are very few colour developing agents that can be used successfully to produce coloured dye images. Also, the dyes which these colour developing agents produce have poor stability to light and are susceptible to heat, humidity, and chemical fumes, even in dark storage e.g. colour prints in an album.
Because Silver Dye Bleach materials do not have to generate a dye image by processing the material in a colour developer, there is far more choice of dyes which can be included in the three light sensitive emulsions. Cibachrome Print and Transparent materials contained dyes of the polyazo type, having excellent resistance to dye fading, humidity and chemical contamination.
Another advantage was a gain in print sharpness. There was a significant gain in sharpness in a Cibachrome print compared to a print made on conventional colour development paper such as the Kodak Ektachrome range papers. This gain in sharpness was due to minimal light scatter, or irradiation, within each emulsion layer. In this context, Irradiation is light scatter within silver light sensitive emulsion layers. Light is scattered by reflection and spreads as it passes through overlapping silver grains in any light sensitive photographic material, film or paper. It causes unsharp images, as the light is spread out and definition suffers.
Each light sensitive layer in a Cibachrome material had a dye of the opposite colour to that layers sensitivity included in the layer. The coloured dye had a masking effect on any light scatter within the emulsion layer. For example, the magenta dye in the green sensitive layer neutralised any scattered light in that layer by rendering it magenta, the opposite colour to green, and therefore the opposite colour to the layers sensitivity.
Acutance dyes were included in conventional colour materials, films and papers, to improve definition, but acutance dyes in Silver Dye Bleach materials are taken to an extreme level, hence greatly improving definition.
Cibachrome could be dish processed, but at no more than one sheet at a time in a processing dish. The support base was fairly rigid, slightly thicker than the base of a resin coated colour printing paper, and did not bend easily. Because of the risk of the corners of one sheet damaging another, interleaving agitation of more than one sheet was not recommended.
Cibachrome Print material was to be handled in total darkness, or under a safelight fitted with a 15 watt bulb and a Dark Brown filter, such as Ilford 912. The near equivalent safelight filters which were suitable included Kodak Wratten 10H, and Agfa 166M, later known as 08.
This Process P-7A processing sequence was in use for Cibachrome Print (CCP) in 1969.
Total time: 47 minutes.
Transparent CCT-D 661
P-10 Process for Cibachrome Print CCP-D 182 and Cibachrome Transparent
Total time: 36½ minutes.
P-18 Process for Cibachrome Print CCP-D 182
Because of the simultaneous action of the combined Dye Bleach and Silver Bleach, the working temperature of this solution was less critical. Plus or minus 2°F could be allowed for the Bleach Bath and Fixer.
The P-18 process was suitable for one shot processing in small cylindrical drums, such as the Simmard, Kodak Printank, the Wilkinson processor and others. Dish processing was not recommended, but could be employed for very large prints which might not fit into a drum. The processing times remained the same for drum, dish, or large continuous processing machines, such as the Kreonite, or Colenta machines.
Cibachrome Transparent CCT D-661 was not compatible with Process P-18, and laboratories printing on CCP D-182 and CCT D-661 either had to carry on processing both materials in the old P-10 process, or run two separate processes.
The three solutions were supplied in concentrated liquid form to make 25 litres of working solution, the Developer and Bleach as two parts each, A and B, and the Fixer as one part. According to W.D.G. Cox, writing in the British Journal of Photography Annual (BJPA) for 1977, it was possible to make up as little as 1 litre of Bleach or Developer working strength solution by taking 200 ml of part A and 100 ml of part B, and mixing these parts with 700 ml of water. He gave no indication of how to make a working solution of Fixer, but as the Fixer was supplied as a one solution concentrate, it might be assumed that 300 ml of Fixer concentrate was mixed with 700 ml water to make the working solution.
For large scale users, solution replenishers were available, again as concentrated liquids, to make 50 litres of each replenisher.
Total time: 16½ to 19½ minutes.
and Process P-12
In 1974 there were very few colour printing materials for making colour prints directly from colour transparencies. The best known material was Kodaks Ektachrome RC paper, Type 1993. The paper was not readily available to the amateur photographer, nor were the Ektaprint R5 processing chemicals, (see Ektachrome paper section).
Although the minimum size of Ektachrome RC paper was 8 inches x 10 inches, and the packets of 25 sheets could be obtained by order through a photographic dealer, the minimum quantity of 5 gallons of each component of the Ektaprint R5 processing chemicals would have been likely to deter even the most enthusiastic amateur photographer from reversal colour printing.
20 sheets of Cibachrome-A print
material, size 8 inch x 10 inch.
These kits would have appealed to amateur photographers who had already done some negative-positive colour printing. They would already have owned some colour printing filters and maybe some of the other equipment. Cibachrome A material could equally well be processed in dishes, like black and white prints, although Ilford did not recommend this method of processing.
Cibachrome-A print material was available in various sizes up to 16 inch x 20 inch. An 11 inch x 14 inch size was sold in the USA and Canada. The almost equivalent size being sold in European countries was 16 inch x 12 inch. The 16 inch x 12 inch was a useful size as two 8 inch x 10 inch prints could be printed on one sheet.
To encourage amateur photographers to start making their own colour prints, especially those who were economically minded and objected to paying for a large size 8 inch x 10 inch kit, Ilford introduced Cibachrome Discovery kits in the USA in 1977. The kit was a smaller version of the 8 inch x 10 inch kit and contained 20 sheets of 4 inch x 5 inch Cibachrome-A print material plus a mini 4 inch x 5 inch processing drum. Also included were the set of printing filters, slightly smaller at 3 inches square, measuring cylinders and processing chemicals to process the 20 sheets of 4 x 5 inch paper.
Cibachrome-A kits were being sold in European countries by 1976. It seems the "Discovery" kits were sold in Europe (presumably including the UK) from 1978. They were known as Cibachrome Mini Kits, but included the same contents as the US "Discovery" kits.
Economically, the kits were an excellent buy for any amateur photographer who had no previous experience of colour printing, and was not keen to spend too much money in case they found colour printing too difficult and found more pleasure from making black and white prints.
The huge advantage of the Cibachrome-A process was that the complete beginner could make prints from colour transparencies and not colour negatives. The filtering, i.e. changing the colour balance of the print, was much more logical than printing from negatives. When printing from transparencies, a colour cast was always corrected with a filter of the opposite colour to the cast. There was the added advantage of using the transparency as a colour guide. If the transparency had a definite colour cast, something easily seen in a transparency but very difficult to detect in a colour reversed negative, a filter of the opposite colour to the cast could be added to the filter pack for a first test strip for an improved colour balance in the print.
print material CCP-A 182E
The material was designated CCP-A 182E. It was only available in a highly glazed surface, similar to Kodak's colour printing papers of surface F.
To assist the printer in achieving the correct colour balance, basic filtrations for four types of reversal films were printed on the back of every packet or box of Cibachrome-A material. Generally the filtrations were made up of yellow plus cyan units, such as 60 40, (60 yellow, 0 magenta, 40 cyan), and it was recommended to expose a first test strip using one of the filtrations given, appropriate to the make of transparency being printed. The filtrations given were only a starting point, and it was extremely unlikely that a correctly balanced print would result from the first trial.
The filtrations printed on the packets could also be used to calculate the differences in colour balance between different batches of Cibachrome-A paper.
When filtering Cibachrome-A material, large changes in filtration were often necessary. Unless the print was extremely close to the correct balance, changes of less than 10 units of any colour would not be enough to make any significant difference to the colour balance. A strong cast could be corrected by a 40 unit Cibachrome filter (or equivalent Kodak colour printing filter).
This process is for processing in the drums provided with the kits. There was a choice of three processing temperatures.
Load drum in total darkness.
Total times: 13½, 12 and 10½ minutes (excluding drying time).