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  1. #1
    Vlad Soare's Avatar
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    Residual Iron Test

    Hello,

    Is there a quick and easy test for residual iron in iron-silver processes?
    I'm thinking of something similar to Kodak HT-2: put one drop on the print, wait a couple of minutes, assess the color of the stain, the end. Ideally, it should detect both iron(II) and iron(III).

    Thank you.

  2. #2
    Marco B's Avatar
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    Quote Originally Posted by Vlad Soare View Post
    Hello,

    Is there a quick and easy test for residual iron in iron-silver processes?
    I'm thinking of something similar to Kodak HT-2: put one drop on the print, wait a couple of minutes, assess the color of the stain, the end. Ideally, it should detect both iron(II) and iron(III).

    Thank you.
    Yes, there is, I mentioned it in my "Long term stability of Pt/Pd prints on paper" article in the Articles section of APUG:

    - Use Bathophenanthroline Indicator Paper for testing for remaining Fe2+ (will not detect Fe3+, but see the remark about using ascorbic acid for reducing Fe3+ to Fe2+ in the instruction PDF below) and thus for effective clearing in Platino/Palladiotypes. These indicator strips are used in the paper conservator world, and it seems they might potentially be a valuable new instrument for Pt/Pd printers. They seem to be very sensitive, capable of detecting just 1ppm (part per million) Iron according to what I read.

    The usage of Bathophenanthroline Indicator Paper is described in the PDF I attached that came from the Iron Gall Ink Corrosion website, see this page particularily.

    They can be bought at: http://www.preservationequipment.com called "Iron Gall Ink Test Paper":
    http://www.preservationequipment.com...Ink-Test-Paper
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    Last edited by Marco B; 03-30-2011 at 05:32 AM. Click to view previous post history.
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    Marco B's Avatar
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    I now noticed there are two more interesting articles on the usage of the iron indicator paper, including good images, here:

    http://www.irongallink.org/images/fi...%20artikel.pdf
    http://www.irongallink.org/images/file/icom14_161.pdf

    Marco
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  4. #4
    Vlad Soare's Avatar
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    Thanks, Marco.
    I was hoping for something easy to mix at home from common chemicals, but I guess this test paper should work just as well.
    I'm not very sure about the way it works. You place a moist test paper strip on the print, and if any Fe(II) ions are present anywhere within the depth of the paper they will all migrate to the surface and react with the test strip? Why would they do that?

    How about residual iron(III)? That can be as damaging as iron(II). Is there something to detect it?

    Edit: OK, I had missed the remark about using ascorbic acid to convert it to Fe(II). If I understand correctly, all you have to do is put some ascorbic acid on the test paper, and it will start detecting Fe(III) as well, right?
    Last edited by Vlad Soare; 03-30-2011 at 05:51 AM. Click to view previous post history.

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    Marco B's Avatar
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    Vlad, please take some time to carefully read the PDF I attached, and all the information about these test strips on the Ink Corrosion website I linked, and the other links in my second post. I think there is enough information and a lot of explanatory images there about how to exactly use it.

    I haven't used this stuff myself yet... just found the very interesting link to ink corrosion where it was mentioned. I don't think there is any other reliable or easy way to do this yet, except for full scale chemical analysis using true laboratory style equipment.

    Even Mike Ware, who is an expert on this kind of stuff, wasn't yet aware of the Bathophenanthroline Indicator Paper, when I mentioned it to him in an e-mail conversation.
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    Marco B's Avatar
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    Quote Originally Posted by Vlad Soare View Post
    Edit: OK, I had missed the remark about using ascorbic acid to convert it to Fe(II). If I understand correctly, all you have to do is put some ascorbic acid on the test paper, and it will start detecting Fe(III) as well, right?
    Seems so:

    "To test for the presence of Fe(III) ions, a drop of 1 per cent (w/v) aqueous
    solution of ascorbic acid was added to the test strip after it was removed from
    contact with the textile. The test strip used for the Fe(II) ion test was cut in half
    before adding the ascorbic acid to one half. Thus results for both tests could be
    compared and retained."

    from the article:

    http://www.irongallink.org/images/file/icom14_161.pdf
    My website

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    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

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    Marco B's Avatar
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    Quote Originally Posted by Vlad Soare View Post
    I'm not very sure about the way it works. You place a moist test paper strip on the print, and if any Fe(II) ions are present anywhere within the depth of the paper they will all migrate to the surface and react with the test strip? Why would they do that?
    I realized I hadn't commented on this remark.

    I can also turn this question around by saying:

    "Why would the Fe(II) ions be present anywhere in the paper?"

    You are using a sensitizer applied to one side of a sheet of paper. Most likely, the bulk of the iron sensitizer is in the top layer of the paper on the side you coated it. So testing there, should give a good indication of any remaining non-cleared iron, as the concentration will be highest there. If it is OK there (properly cleared), it will be OK deeper down in the paper, and on its non-coated side.

    Of course, the free iron ions don't magically move to the test strip. The moistened test strip just picks up on tiny amounts of the ions, and since it is already sensitive enough to detect 1 ppm iron, it will detect trace amounts of the non-cleared iron sensitizer.

    Also note that, according to the instructions, you need to apply some pressure to the moistened test strip when bringing it in contact with the sample you want to test (your alternative process print), which will ensure it picks up any soluble free iron II and III ions.
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    Marco B's Avatar
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    One last remark:

    Using the ascorbic acid to reduce Fe3+ to Fe2+ is probably vital to the usefulness of this test paper for alternative processes using an iron based sensitizer. Since the Fe2+ acts as the electron donor while reducing for example Ag+ silver ions to Ag metallic silver, or Pt/Pd ions to their respective metals, most of the remaining non-cleared iron will be Fe3+ in those areas that have a visible image (paper whites inside the coated areas will still have Fe2+ if not removed properly in the clearing step, since no oxidation/reduction process took place there).
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    "I don't know, maybe we should disinvent color, and we could just shoot Black & White." - David Burnett in 1978

    "Analog is chemistry + physics, digital is physics + math, which ones did you like most?"

  9. #9
    Photo Engineer's Avatar
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    These tests will work for soluble Iron salts, but there is no good test for insoluble iron salts. Fortunately for us, they are either inactive or show up as a visible brown stain. There is only one method to remove the brown stain AFAIK. IDK how it might affect your images though.

    PE

  10. #10
    Vlad Soare's Avatar
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    I'm not very sure about the way it works. You place a moist test paper strip on the print, and if any Fe(II) ions are present anywhere within the depth of the paper they will all migrate to the surface and react with the test strip? Why would they do that?
    [....]
    You are using a sensitizer applied to one side of a sheet of paper. Most likely, the bulk of the iron sensitizer is in the top layer of the paper on the side you coated it. So testing there, should give a good indication of any remaining non-cleared iron, as the concentration will be highest there. If it is OK there (properly cleared), it will be OK deeper down in the paper, and on its non-coated side.
    I don't know. I'm not so sure. The bulk of the sensitizer may indeed be in the top layer after coating, but washing and clearing proceed from top to bottom. I think that the outermost layers clear quite quickly, while extensive washing is necessary to remove the sensitizer embedded deep into the paper. I may be wrong about this, but I suspect that those ferric/ferrous ions absorbed deeply into the paper cause damage to the image in time, and not those lying at the surface (which are probably eliminated during the first stages of the wash). At least that's how I imagine it. But I may be missing something...

    There is only one method to remove the brown stain AFAIK. IDK how it might affect your images though.
    You mean a pair of scissors?
    Last edited by Vlad Soare; 03-31-2011 at 01:29 AM. Click to view previous post history.

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