Residual Iron Test

Discussion in 'Alternative Processes' started by Vlad Soare, Mar 30, 2011.

  1. Vlad Soare

    Vlad Soare Member

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    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. Marco B

    Marco B Member

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    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
     

    Attached Files:

    Last edited by a moderator: Mar 30, 2011
  3. Marco B

    Marco B Member

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  4. Vlad Soare

    Vlad Soare Member

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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? :confused:

    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?
     
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  5. Marco B

    Marco B Member

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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.
     
  6. Marco B

    Marco B Member

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    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
     
  7. Marco B

    Marco B Member

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    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.
     
  8. Marco B

    Marco B Member

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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).
     
  9. Photo Engineer

    Photo Engineer Subscriber

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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. Vlad Soare

    Vlad Soare Member

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    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... :unsure:

    You mean a pair of scissors? :D
     
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  11. Marco B

    Marco B Member

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    Vlad,

    Look at the third page of PDF added here, a page from James M. Reilly's "Care and identification of 19th century photographic prints". It shows cross sectional electron microscope views of real salted paper and a platinum print. Please note the electron microscope images only represent the top layer of the paper, as depicted by the schematic drawings and the accompanying text also.

    Although there is clearly some deeper penetration of the image forming particles and thus the sensitizer, the bulk will be in this top layer of the paper. I really see little reason to assume there may be much iron left in the deeper layers, if the top layer tests fine using the iron test strips.

    Anyway, whatever the situation, the fact that you are even planning to test it, is already an improvement over what most other alternative process printers do. Since not many are aware that it is possible to test this, most I think simply assume that sticking to their current workflow, working consistently, and using fresh chemicals, will ensure they will be safe in terms of proper clearing of the sensitizer.

    If good practices are being applied, that actually (and hopefully) may not be such a bad assumption.

    Of course, it still would be nice if a couple of APUG alternative process printers reported back on their exact workflow, and started testing proper clearing with the Bathophenanthroline Indicator Paper. If they than report their results here on APUG, with hopefully no issues, we really know current best practices are sufficient.

    Any detected issues with non-cleared iron, will of course be interesting too. We may all learn something.

    Link to PDF with electron microscope images of alternative process prints

    Marco
     
  12. Photo Engineer

    Photo Engineer Subscriber

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    There is a rare and usually non-destructive method that can be used to remove brown stains caused by insoluble iron salts.

    PE
     
  13. Marco B

    Marco B Member

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    You're starting to sound a bit cryptic lately, PE :blink:

    Any more useful information besides that it is "rare" and "non-destructive" (so the scissors are out :wink:)
     
  14. Photo Engineer

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    Marco;

    Sorry, I did not think I was being cryptic as I had posted it so many times here on APUG. The Dequest series of sequestering agents have such a powerful complexation constant with Iron salts that they can even dissolve Iron (II and III) oxides and hydroxides. So, there is the direct answer for about the 10th time.

    Have fun.

    PE
     
  15. Marco B

    Marco B Member

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    That I now read for the first time! With over 1 million posts on APUG, and almost 18.000 by yourself :wink:, you can't expect us to always know where to search for this stuff... not even taking into account that many people, including myself in this case, wouldn't even be able to remotely figure out what keywords to search on.

    "Sequestering agents" is a new term for me.

    Thanks for the answer!
     
  16. Photo Engineer

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    Marco;

    No problem. I am often blinded by the facts you have posted, and you must realize that a great proportion of my posts are re-posts. Sorry.

    PE
     
  17. Vlad Soare

    Vlad Soare Member

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    Thanks, Marco. I'll try to get some test paper and will report how it works.
     
  18. Marco B

    Marco B Member

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    If you are going to test it seriously, maybe it would be good to design a work plan for the test, to get a more meaningful controlled result.

    For example, here are a couple of things to think about:

    - Since the test paper without use of ascorbic acid only detects Fe2+, there may potentially be a difference in the readings from different parts of a prints. Since the sensitizers Fe2+ is converted back to Fe3+ while reducing silver or Pt/Pd ions to their respective metals, there might be a difference between a test result in the shadows versus the highlights of a print (higher reading of Fe2+ in midtones/highlights, and lower reading in shadows where sensitizer iron was "used up" during the reaction). On the other hand, since Fe2+ is only formed from the original Fe3+ in the sensitizer due to the UV exposure applied, highlights and midtones may not show a real difference compared to shadows, as they receive less exposure. Anyway, maybe it would be an idea to use a real exposure step wedge to see if you get different readings while going from highlights to shadows. But of course, since you are clearing the prints, we actually assume (and hope), you will not get readings of remaining iron at all.

    On the other hand, according to this article and research by the Getty Museum on the Alternative Photography website, all prints, even the best processed ones, have trace iron:

    "To date we haven’t found any iron-based prints that do not contain some residual iron even after very good processing, but our analysis of Steven’s prints showed that his prints will be very stable with minimum chance of tonality changes due to iron residue."

    - Maybe it would be good to have some control readings, so cutting up a test print in sections and giving them different treatments might be an idea:

    * Use an uncoated part of the paper as control. It shouldn't have iron at all, but it might be interesting to put it through the whole developing/clearing/washing cycle to see if it doesn't pick up on anything.

    * Use a coated but undeveloped/uncleared piece of paper. Of course, since you didn't clear it, it should be full of iron sensitizer.

    * Make dilutions of your normal working strength clearing bath, and than use your normal work flow and clearing time to test how critical / sensitive the strength of the solution is, e.g.:

    - Undiluted
    - 6:1 (clearing bath:water)
    - 5:1
    - 4:1
    - 3:1
    - 2:1
    - 1:1
    - 1:2
    - 1:3

    It should give an idea of what happens when the clearing bath gets exhausted, in this case down to 1/4 of its original strength (the 1:3 dilution). Of course, diluting it is not the same as true exhaustion / use, but it gives and idea.

    - Of course, as suggested in some of the PDF I linked, it is always good to cut up each piece of used Bathophenanthroline Indicator test paper into two parts, applying the ascorbic acid to one but not the other, to see if, and how much, of a difference you get for Fe2+ alone, or Fe2+ and Fe3+ combined.
     
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