The film remained cut into 6 x 6 transparencies, being held up to the light for viewing and stored in a film envelope. 2¼ square projectors were extremely expensive.
When scanners first became available, our photographer was kitted out with a flat-bed and transparency hood (and the horrible SCSI card). Because these Dufaycolors had photographs of family members, I asked him to scan them so that they would be safe from deterioration or loss.
I only remembered that I had not told him something important about Dufaycolor when the scans were done and I looked at them on screen. They were reversed left to right. That's because he scanned them as one does any other film or transparency - looking at them from the shiny side. But Dufaycolor was different - you have to view them from the dull (emulsion) side.
I give links to websites explaining Dufaycolor below, so what follows is a resume. On the film base was printed a very fine pattern consisting of transparent blue and green squares or rectangles and red lines. The method of producing this array (reseau) of red, blue and green (shown in one of the websites) was ingenious and must have been the result of extensive experimentation both with the optimal pattern and the printing (the reseau is not that unlike a Bayer screen used in a modern digital camera) A normal panchromatic film emulsion was then added. In order to achieve colour separation the emulsion was exposed through the base. In the camera, the shiny side faced the lens, not the emulsion - the opposite of normal. That's why Dufaycolors have to be viewed or scanned from the dull side.
Exposing through the base and the printed reseau brought other problems, especially low transparency, so that a much more powerful projector was needed. Projection also enlarged the reseau and it became visible to the audience in a cinema (a few feature films were made with Dufay 35 mm stock) with anything other than a relatively small screen.
The speed was about 8 ASA (or ISO if you must), about the same as most colour films of the time.
Dufaycolor soon lost ground to the new, subtractive, colour processes exemplified by Kodachrome.
My transparencies do not appear to have deteriorated to any noticeable extent in over 50 years probably because they have not been exposed to light. Information available does suggest the rapid fading of Dufaycolor transparenies in light, especially in a powerful projector.
A couple of years ago, I re-scanned my twelve transparencies in an Epson V500. One of them is shown below along with details of the reseau scanned from small areas of the transparency.
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| Dufaycolor 6 x 6 Transparency - probably late 1957 |
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| Dufaycolor - magnified to show the reseau. Top is parallel to edge of film (left hand side of photograph above) |
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| Dufaycolor - magnified to show the reseau. Top is parallel to edge of film (left hand side of photograph, top) |
Dufaycolor was a French invention developed — ultimately to little avail — by British companies. I did not realise when I walked the dog past the Spicer's paper factory at Sawton, near Cambridge, many years ago that the plant had been the site of secret work to develop Dufaycolor after Spicers bought the process from Louis Dufay in 1926 and before the greatly improved version was launched in 1931.
I had also forgotten that, according to the BJ Almanac of 1956, each box was coded to indicate whether film from a particular batch needed standard exposure, one stop more or one stop less than the indicated exposure. Why they did not just show the speed rating in BS, ASA, DIN, Scheiner or Weston for the particular batch (i.e. 4, 8 or 16 ASA) I do not know.
My twelve transparencies are my only experience of Dufaycolor. They have created interest in this old additive colour process over the years. But if you have scanned slides and the men have breast pockets on the right and the women are buttoned up the wrong way, you may have found some Dufaycolor transparencies.
Links (well worth reading)
http://www.pathefilm.freeserve.co.uk/95flmart/95dufay.htm
http://www.photomemorabilia.co.uk/Ilford/Dufaycolor.html
http://www.retouchpro.com/forums/history-conservation-repair/34149-dufaycolor-scanning-restoring-archiving.html
http://www.aiccm.org.au/docs/Bulletin2008/Vaughan_Bulletin_2008_Vol31.pdf
http://www.brianpritchard.com/Dufay.htm
http://www.oldandsold.com/articles21/color-photography-10.shtml
