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  1. #11

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    PE,

    The book is by Jaromir Kosar, Light-Sensitive Systems: Chemistry and Applications of Nonsilver Halide Photographic Processes. John Wiley and Sons, New York, 1965.

    Great section on dichromate colloid systems.

    Sandy

    Quote Originally Posted by Photo Engineer
    Donald;

    After all, if cuprous oxide works, what else is out there. I think that the field is open for a good investigator and suggest that you look for the book by Khosar or Kosar, I forget the spelling OTOMH. Fascinating book on alternative processes. I have read it cover to cover and unfortunately have forgotten most of it due to disuse and time. Everyone wanted Ag emulsions and not these 'old fashioned' dinosaurs. (well, now here we are with 'rex')
    ng with cyanotypes myself right now, trying to tweak some things.

    PE
    Last edited by sanking; 02-26-2006 at 10:26 PM. Click to view previous post history.

  2. #12
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    Thanks Sandy, I just could not remember that last night.

    I had a copy on loan from the KRL Library and turned it in when I retired.

    PE

  3. #13
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    I've got to pick myself up some green ferric ammonium citrate; it's cheap as I recall ... but the shipping cost will be annoying - time to find local chemistry suppliers.


    Donald, when you try this out, definetely let us know; cyanotypes fast enough for in-camera or especially for the enlarger would be really nice; I wonder if you could coat this stuff onto a clear base or render the paper base transparent (with oil or such) and print from the cyanotype negatives from in camera ...

  4. #14

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    There is a problem with ferrogallate ink in that over time it destroys the paper on which it appears. Correspondence from the Civil War have the centers of loop letters such as "o" and "l" falling out. This would serious limit the usefullness of photographs made by the process described.

  5. #15

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    My understanding is that with iron-based inks, since they used iron sulfate (aka vitriol), which when combined with the tannic acid would release sulfuric acid. It is this sulfuric acid that would, over time, digest the fibers in the paper.

    Perhaps a wash of the print with a buffer would help with this.

  6. #16
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    Quote Originally Posted by Donald Qualls
    PE, not to argue, but the recent work on cyanotype rex has demonstrated in-camera negatives, cyanotype-to-cyanotype contact printing (through heavy paper), and exposure of prints with ordinary tungsten light. The very same chemicals are vastly faster (based on my reading, it looks like several stops faster) when the sensitive iron and the colorant are separated; my hypothesis (as a non-chemist) is that light energy goes to reducing ferric to ferrous without being soaked up in the secondary reaction or absorbed by its products -- which might reasonably mean both less energetic (i.e. longer wave) light can do the job, and a great deal less of it is needed.
    I don't mean to butt in, but Mike Ware does explain the ferric process on his website. I seem to recall, that Fe3+ reduces only in the presence of UV light, not regular light. In lieu of any materials on the C. rex process, I would lean on previous scientific data. Actually, Hershel did try ferric ammonium citrate by itself, and developed in various things (including potassium ferricyanide and gallic acid). His conclusion was that the citrate by itself was too slow. Oxalate might be a different story. And don't get me wrong. If the cyanotype process was faster this way, I would be near the front of the line on getting at it. But I also think that both Herschel and Ware have researched the cyanotype very thouroughly. I don't mean any of this in a mean way, just disseminating info. No hard feelings?

    The Unblinking Eye has a variation on the cyanotype with gallic acid if I remember rightly.

    Drew
    "But what is strength without a double share of wisdom." --John Milton

    "Our greatest fear should not be of failure, but of succeeding at something that doesn't really matter." --Unknown missionary

  7. #17
    Donald Qualls's Avatar
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    Quote Originally Posted by Dracotype
    I don't mean to butt in, but Mike Ware does explain the ferric process on his website. I seem to recall, that Fe3+ reduces only in the presence of UV light, not regular light. In lieu of any materials on the C. rex process, I would lean on previous scientific data. Actually, Hershel did try ferric ammonium citrate by itself, and developed in various things (including potassium ferricyanide and gallic acid). His conclusion was that the citrate by itself was too slow. Oxalate might be a different story. And don't get me wrong. If the cyanotype process was faster this way, I would be near the front of the line on getting at it. But I also think that both Herschel and Ware have researched the cyanotype very thouroughly. I don't mean any of this in a mean way, just disseminating info. No hard feelings?

    The Unblinking Eye has a variation on the cyanotype with gallic acid if I remember rightly.
    Drew, what you're saying above is the accepted wisdom on iron-based processes, no question. It was in examining how Herschel originally did his prints (coating the sensitive iron alone, then developing with the colorant) that the current workers came to the rex processes; beyond that, I'm only repeating the claims they've made. I haven't done it yet -- perhaps in the next day or two, having completed my camera repair and conversion work today.

    HTML, waxing paper negatives (from the back) was standard practice for decades, back when kallitypes in camera were competing with Daguerreotypes. It *might* be possible to coat c. rex on inkjet transparency material -- certainly worth trying, I'll have to see if I have a box of that stuff around the house. Those who created c. rex report being able to contact print from c. rex negatives back to a positive in the same medium, but (again) haven't published whether they waxed the original or otherwise rendered it translucent.
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  8. #18
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    It *might* be possible to coat c. rex on inkjet transparency material -- certainly worth trying,
    Why use inkjet transparency film? Why not try a sheet of fixed-out sheet film? Perhaps let the chemistry soak into the gelatin base?

  9. #19

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    Quote Originally Posted by htmlguru4242

    SO, if a light-sensitive iron compound (ferric ammonium citrate, ferric oxalate, etc., etc.) were coated onto a paper and exposed to light, therefore reducing some of the iron to ferrous, and the paper was then soaked in or coated with gallic acid / tannic acid / gallotanate, etc., would an image not be produced?

    Do I have a good idea, has this been done before, or am I WAY off?
    To get back to your original question, here's one answer. If you expose a cyanotype and don't wash it, but dip it first in a solution of tannic acid, the whole sheet will turn black. I've tried this. Judging by this experiment, tannic acid does not discriminate between Fe3+ and Fe2+. It shouldn't matter whether you use citrate or oxalate.

    I imagine gallic acid would work the same way, since the distinction between the two acids seems quite vague. Also, judging by the use of tannic acid in conservation as an antirust agent, it would make sense for it to bond with all forms of iron.

  10. #20

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    PE

    Do you have any suggestions in the open literature concerning the copper-oxide system? J. Phys. Chem. B would be fine. :~)

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