Color process : trichromy, Ducos du Hauron, colored mica sheets

Hello,

I'm looking for information on a type of color process that seems particularly rare. The object image consists of two sheets of mica (approx. 5 x 6 cm) superimposed on a thin frosted glass. The image is revealed by the juxtaposition of two colored layers (magenta and yellow). It apparently lacks the third layer of cyan to perfect the rendering of color.

The trichromy process was revealed by Louis Ducos du Hauron in 1869. In his statement he also proposed a solution to use mica (good for its low thickness and transparency) as a picture.

Today, I would be willing to learn if some collections around the world and especially in France has similar examples of this technique.

Thank you very much for the help you can provide me.

PAK

I think the use of thin mica was because cellulose acetate, or nitrate film base was not invented yet, and he needed a thin transparent material so the superimposed images would register fairly well together. There have been a number of processes that create separation negatives and positives using 2 or 3 primaries to achieve a relatively complete color record. As early as the process you reference is, I am surprised he could come up with a panchromatic emulsion to shoot the negatives with.

Would you be so kind to mention the processes, this is something I am currently very interested in and any reference or process, using RGB or CMY and separation negatives would be of great interest

thanks

PHOTOTONE said:

I think the use of thin mica was because cellulose acetate, or nitrate film base was not invented yet, and he needed a thin transparent material so the superimposed images would register fairly well together. There have been a number of processes that create separation negatives and positives using 2 or 3 primaries to achieve a relatively complete color record. As early as the process you reference is, I am surprised he could come up with a panchromatic emulsion to shoot the negatives with.

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Dear Bob,

Thank you for your interest.

It is quite easy to find on the Internet a statement of the Ducos du Hauron's technical to reproduce 3 positiv colors.
With the condition to read a little french I will recommend the very interesting website of Constantine Imbs.

http://brevetsphotographiques.fr/englishformulairecontenu.asp?cleprimaire=65100
http://brevetsphotographiques.fr/english.htm
http://books.google.fr/books?id=bpMcg2S-IaoC&printsec=frontcover#PRA1-PA3,M1

Best regards,

PAK

Bob, a bit of a late reply, but there is an excellent article at this address about colour separation and filtration. There are other articles, but the site is in French, the article referenced is at least visual, and illustrate admirably effect of the different variations of filtration on colour separation.

http://trichromie.free.fr/trichromie/index.php?post/2009/05/13/Colorimétrie-Trichrome

Best

Delphine

PHOTOTONE said:

As early as the process you reference is, I am surprised he could come up with a panchromatic emulsion to shoot the negatives with.

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Vogel found spectral sensitization in 1873, but still it took him untill 1884 to get somewhat panchromatic. 1902 would be the birth of the panchromatic plate.

However, when you make successive colour seperations speed is not that much an issue and Ducos du Hauron could start into the red in the mid 70's.

You could use very fine mica powders which have been coated with TiO2 to different thicknesses and are interference pigments. Try coating a glass plate and doing a 3 color gum arabic print with interference cyan, magenta, and gold micas. View against a black background.

Sorry, that was random.