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  1. #1
    htmlguru4242's Avatar
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    Fisher Couplers - What Exactly are They

    No sure if this belongs here, but i was reading up on the history of color photography (because old chemistry fascinates me), and I can across somethign about Rudolph Fisher's couplers, which he deisgned in 1912. Does anyone know what chemicals these were / what was used to develop them. Like most old color processes, I'm assuming that this can't be easily replicated now, but it still would be neat to see what they were. Anybody know?

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    "If one wishes to examine the transition from Technicolor to Eastmancolor and other color coupler type neg-pos color processes you have to go back to the work of Rudolf Fischer in 1911 who discovered that 'certain dyes can be formed when silver bromide is developed with p-phenylene together with coupling substances' (for more information see COLOR CINEMATOGRAPHY by Adrian Cornwell-Clyne, 3rd edition, 1951, pages 355-388)"

    From http://www.cinematography.net/Pages%...ilmsOn5254.htm

    "Colour film uses similar principles to black and white, but with a few added complications – the information that is the same as for black and white film will not be repeated, only the “extras” will be discussed. The development process used today for colour negative film is referred to as chromogenic. Rudolph Fisher patented the dye coupler process used for colour film in 1912, and it was he who invented this word/name."

    From http://www.nsac.ns.ca/envsci/staff/j...er2/Films.html

    So it looks like C-41 and RA-4 are the current generation of this process. Learning more about them would give info on the couplers used. Developers would be CD-4 or related compounds these days?

    Kirk - www.keyesphoto.com

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    htmlguru4242's Avatar
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    Thanks Kirk! Good Info.

    I am aware that it was the basis of today's chromogenic color films, and for processes like Kodachrome. It's good to know what the developer was ... However, I've still been able to find info. on the chemical composition of hte couplers ...

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    Kodachrome does not use Fischer couplers, nor did it ever use them AFAIK.

    Please look up my previous posts on Fischer couplers here on APUG. Basically, Fischer couplers contain carboxylic acid or sulfonic acid groups on them. The contain COOH or SO3H groups which render them soluable in the emulsion when coated.

    The couplers currently in use which are totally non-polar were invented by W. T. Hanson and P. W. Vittum and are named Kodacolor couplers. They are the only ones in use today in current products.

    The generic coupling reaction was discovered by Fischer. This was not reduced to practicality until Agfacolor and Kodachrome were realized in the 30s. Otherwise it was mainly a lab curiosity looking for a product.

    Abandonment of the true hydrophylic Fischer couplers was made necessary by the introduction of high speed multiple slide coating which was badly affected by the rheological properties of the Fischer couplers. Today's couplers are only similar to those of Fischer in terms of forming dyes from coupling at an active methylene site with a p-phenylene diamine developer.

    Yellow couplers tend to be acetoacetates, magenta couplers are generally pyrazolones, and cyan couplers are generally phenols or napthols. The increasing level of conjugation in the molecule shifts dye hue from about 450 to 550, to 650 respectively.

    PE

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    htmlguru4242's Avatar
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    Oops, unlcear wording again. I was not sayign that Fischer couplers are used in current color products. I was simply trying to say the coupler concept has developed into what we have today ...

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    Kirk;

    CD4 is a hydroxy ethy ppd, but CD3 is a methane sulfonamido ethy ppd. They differ hugely in polarity, activity and dye hue when they couple with a given coupler. They also yield vasty different dye stability with a given coupler.

    Therefore, it is not good to exchange the two, especially if image stability is desired. Endura, processed in a CD4 developer will show marked degradation in dye hue and markedly worse dye stability (last I tested it anyhow). I had a long mail correspondance with Pat Dignan years ago on the subject and that helped initiate some of his tests way back when.

    CD6 and CD3 give a good match for dye hue and somewhat better dye stability, with CD6 having the approximate activity of CD4 - higher than CD3. Therefore, you could get a much more active developer (like using CD4) but without the sacrifices of CD4 by using CD6. Try getting some though. Nearly impossible!

    Also, the biggest changes are that Fischer discovered a 4, 6 or 8 equivalent reaction in his scheme of things. They often required a follow up oxidant to form the final dye from the leuco dye. Work it out and you will see that is true. Today's couplers are mainly 2 equivalent.

    PE

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    htmlguru4242's Avatar
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    Were the chemicals that you listed for couplers what is curently used or what fischer used?

    If not, does anyone know what it was Fischer used in his testing?

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    Quote Originally Posted by htmlguru4242
    Were the chemicals that you listed for couplers what is curently used or what fischer used?

    If not, does anyone know what it was Fischer used in his testing?
    What I listed was the generic organic class of each of the chemiclas used currently in color photographic products.

    CH3-CO-CH2-CO-R generic Acetoacetate with coupling at CH2.

    This is about the only example I can post without resorting to graphics to show the organic structure, or using exotic chemical names. The above compound forms a yellow dye. The R is a huge ballast group. Fischer just tacked on a sunfonic acid on a benzene ring (IIRC - I have not looked up his precise work, and he did use some cyano compounds where CN replaced the leftmost CH3 above (again IIRC). His work is not studied much nowdays being so obsolete.

    It is like studying Phlogiston theory.

    PE

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    htmlguru, if this stuff interests you, you absolutely need to get your hands on "Organic Chemistry of Photography" by Shinsaku Fujita (published by Springer, 2004). It's expensive, but any good university library should have it. I think you'll find a lot of interesting reading in it.

  10. #10
    htmlguru4242's Avatar
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    Oh crap; a $200+ book ... I'm sure some university libraries would have it ... I'll have to look there, because that's not exactly the type of book they'd sell on Amazon.

    IT sounds good from what I've just read. Thanks!!

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