In the early days of photography, the only way to shoot a colour photograph was by making three separate exposures on monochrome glass plates through three filters – red, green and blue – then to use various devices for combining the images for viewing. The holy grail was to find a way of inserting a glass plate, or a roll of film, into any camera to produce a colour picture with a single exposure. It was 1935 before colour film for use in just about any camera became truly viable. Beating both Agfa and Kodak by just one year, the film was called Dufaycolor, and it was British – well, sort of.

 

The Dufaycolor story began with French inventor Louis Dufay. Following his success with dioptichromes, his next step was to  develop a similar colour matrix on flexible film, aimed primarily at the cinematography industry. His need for an input of cash to make this into a still camera film came from two British companies: Spicers Ltd, founded in 1796 as a paper mill, and Ilford Ltd, founded in 1879 to make dry plates but, by the time of the association with Dufay, also a reputable roll film manufacturer. Both co-operated in the development of Dufaycolor. It was launched as a 16mm cine film in 1932 and as a still photography film in 1935, available as 35mm, 120 roll film and several sizes of flat film. A gelatine filter supplied with each batch of film helped remove excessive blue in daylight. Speed varied with different batches, but was generally around 10 ASA (what we now call ISO).

 

How Dufaycolor was made

The manufacture was a bit complicated. Take a look at the diagram on on the left, taken from The Dufaycolor Book, published in 1935. You’re looking at 100x magnification of the way a grid of lines known as the Dufaycolor réseau was built up.

 

The base of the film was first coated with a thin layer of collodion dyed blue. On top of this, greasy ink lines were printed at an angle to the length of the film roll at a rate of 20 lines to the millimetre and with the space between them being the same width as the lines. The blue dye between the lines was bleached and a new dye turned the spaces green. Then the greasy ink lines were removed, leaving the blue lines originally beneath them in place.

 

At this point, the film consisted of a series of blue and green alternating lines. Across this, a new set of greasy ink lines was printed, at right angles to the first, this time with a broader width and less space between them. A new bleaching bath removed all the blue and green segments apart from those protected by the new greasy ink lines. The clear spaces were then dyed red and the greasy ink lines were removed.

 

 

 

 

 

 

 

 

The result was the réseau, consisting of blue and green lines with red lines diagonally across them. To protect the réseau, a thin layer of varnish was applied, followed by a panchromatic emulsion. These layers were then sandwiched between a transparent film base and a black protective paper cover. In the camera, light from the lens, travelled through the film base, through the réseau, through the varnish layer and onto the emulsion.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How Dufaycolor was developed

Dufaycolor processing agents were set up around the country. The end result was a transparency, and the images were returned mounted in large black frames, often with advice to the user about over- or under-exposure and other perceived faults. Agents also offered a service for turning the colour images into monochrome negatives or black and white enlargements. Duplicate colour transparencies cost 4s 6d (22½p) each.

 

Under the réseau of coloured lines, Dufaycolor was a monochrome film, so it could also be developed by amateur darkroom enthusiasts. Manufacturing chemists Johnson & Sons sold a kit containing everything needed, apart from a small amount of sulfuric acid, available from chemist shops. The film was loaded into a developing tank and chemicals from the kit made up as specified in the instructions. The process went like this:-

 

• Develop for five minutes.

• Brief wash.

• Bleach for five minutes.

• Brief wash.

• Clear the film in bisulphite solution.

• Brief wash.

• Expose for 20-30 seconds 1ft from a 100-watt bulb.

• Redevelop in original developer.

• Wash for 2 minutes.

• Place in a chrome alum hardening bath for 5 minutes

• Wash for 15 minutes.

• Hang up to dry.

 

To understand how that procedure turned out a colour transparency, start by keeping in mind that a coloured filter (in this case the lines on the réseau) passes light of its own colour but blocks light of its complementary colours. Now consider what happened to the red areas of any subject being photographed. Red light passed through the red areas of the réseau, but was blocked by the blue and green areas. This meant that, on development, silver bromide in the emulsion turned into a black silver deposit behind each red filter element, while the silver bromide which lay behind the blue and green parts of the réseau were unaffected. When the film was put through a bleaching bath, it dissolved away the black silver deposits from behind the red parts of the réseau without affecting the unexposed areas behind the blue and green elements. When the film was exposed to the 100-watt bulb, it affected the unexposed areas, rendering them black when redeveloped. Thus there was now a black silver deposit behind both the blue and green areas, while the red area remained clear. So, when the film was illuminated from behind, light was only allowed to pass though the red parts of the réseau and an accurate representation of the red parts of the image was seen. Now apply the same reasoning to the blue and green parts of the subject and the way they were interpreted through the blue and green sections of the réseau. The final result meant the viewer saw the image made up of minute lines of red, green and blue, which appeared to the eye as a full colour image.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

How Dufaycolor was viewed

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