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  1. #11
    Marco B's Avatar
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    Quote Originally Posted by Vlad Soare View Post
    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...
    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
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    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "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?"

  2. #12
    Photo Engineer's Avatar
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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

  3. #13
    Marco B's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    There is only one method to remove the brown stain AFAIK. IDK how it might affect your images though.
    Quote Originally Posted by Vlad Soare View Post
    You mean a pair of scissors?
    Quote Originally Posted by Photo Engineer View Post
    There is a rare and usually non-destructive method that can be used to remove brown stains caused by insoluble iron salts.

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

    Any more useful information besides that it is "rare" and "non-destructive" (so the scissors are out )
    My website

    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "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?"

  4. #14
    Photo Engineer's Avatar
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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

  5. #15
    Marco B's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    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
    That I now read for the first time! With over 1 million posts on APUG, and almost 18.000 by yourself , 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!
    My website

    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "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?"

  6. #16
    Photo Engineer's Avatar
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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

  7. #17
    Vlad Soare's Avatar
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    Thanks, Marco. I'll try to get some test paper and will report how it works.

  8. #18
    Marco B's Avatar
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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.
    Last edited by Marco B; 04-02-2011 at 04:23 AM. Click to view previous post history.
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    "The nineteenth century began by believing that what was reasonable was true, and it wound up by believing that what it saw a photograph of, was true." - William M. Ivins Jr.

    "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?"

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