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  1. #1
    Marco B's Avatar
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    Long term stability of Pt/Pd prints on paper

    NOTE: This is a copy of the last concluding post in a thread I started in the Alternative Process forum here on APUG. I thought it wise to add it here as well, for better accessibility to others.

    *** CONCLUSIONS: ***

    - Despite the noble metals themselves being virtually indestructible (only concentrated hydrochloric or nitric acid will dissolve them), both true Platinotypes (100% Pt), Palladiotypes (100% Pd) and mixtures thereof, can suffer from archival permanence or longevity issues. The main issue is not with the metals and image itself, but with threads to the paper base.

    - There are four main threads to Platinum prints, and three to Palladium prints, the difference caused by the much lesser catalytic activity of Palladium:

    These are:

    * 1) Acidification of the paper through the catalytic activity of Platinum, causing embrittlement of the paper. The catalyic activity of Platinum causes air born SO2 gas to be converted to SO3 and ultimately sulphuric acid (H2SO4) (See Mike's comments here and in his "Chrysotype: Photography in Nanoparticle Gold" article). Acidification leads to the breakdown of cellulose, as it splits the chains and causes depolymerization. Cellulose is the main component of wood and paper. NOTE: this first issue is virtually absent in 100% Palladium prints, due to the much lesser catalytic activity for this reaction, if at all.

    * 2) Breakdown of the cellulose in the paper base of a Pt/Pd print caused by Hydroxyl radical formation as a consequence of retained / uncleared Iron (Fe2+ or Fe3+ cations).

    The process behind this is about the following (from this article):

    Fe2+ + O2 + H+ --> Fe3+ + HOO•
    Fe3+ + HOO• + H+ --> H2O2
    Fe2+ + H2O2 --> Fe3+ + OH- + OH•
    OH• + Cellulose --> depolymerisation

    Where OH• is a highly reactive Hydroxyl radical, as you can see created from the remaining iron in the print. Paper is mainly cellulose, and depolymerisation means the chains of cellulose are broken down in smaller pieces, causing embrittlement of the paper.

    This is not a trivial issue. There are quite a lot of historical examples of retained Iron. In fact, the Getty Conservation Institute, states that all of the Iron based process prints (Pt/Pd, VanDyke etc.) they investigated up to now using advanced X-ray Fluorescence (XRF) techniques, showed some amount of residual retained Iron, even if very good practices were employed for clearing and washing. However, very tiny amounts of retained Iron will probably not pose a major thread to longevity of the prints.

    * 3) Discolouring of the paper base by formation of oxidized Iron (essentially "rust") causing yellow or even dark red stains. The Getty Conservation Institute has witnessed Platinum prints with dark red highlights due to fully oxidized Iron.

    * 4) Discolouring of the paper base by discolouring and break down of the paper fibres themselves. This will mainly occur with low grade lignin containing papers made of (purified) wood pulp, as lignin is even capable of autooxidation (reaction with Oxygen in the air, see "Aging and stabilization of Alkaline Paper"). However, it is likely that retained Iron will or may cause similar issues even on high grade 100% cotton rag paper, via the reaction described in issue 2).

    Nonetheless, use of high quality 100% cotton rag paper - so paper made of cotton instead of wood - should provide good chances for long term survival of the print, since this kind of paper is of a very high almost pure cellulose content. Luckily, this is already common practice among Pt/Pd printers and recommended everywhere.

    This reaction is probably also responsible for the sometimes witnessed "image offsetting" onto cover paper seen with some Pt/Pd prints, whereby a mirror image becomes visible on the cover paper. See Mike Ware's remark below:

    "'Image offsetting' by platinotypes is a well-known and characteristic effect, as illustrated by Jim Reilly and Taylor Whitney. It could be due to two things: the catalytic acid production diffusing across and degrading the opposite contacting sheet, or even to a more direct surface catalysis of the oxidative degradation by air of the polyphenolic lignin macromolecules in some wood-based papers, giving rise to quinoid structures with typical yellow-brown chromophores (same thing that causes colour of oxidised hydroquinone developers, and yellowing of newsprint). There should have been some research on this by now, but I don't have the infra-red instrumentation needed."

    And another example of this:



    *** WHAT CAN BE DONE TO PREVENT ALL THIS? ***

    You may wonder what can be done to prevent all this. Well, the following things may be of help:

    - As said, only use highest quality 100% cotton rag paper, as it is one the most durable forms of paper with a very pure cellulose content and thus practically lignin free. Cotton rag documents have survived from the middle ages in remarkably good condition...

    - Frame all of your Pt/Pd prints behind glass, especially 100% Platinum prints. Although it is probably very tempting to have a matt print like Pt/Pd framed without glass, it will pose a long term thread. Framing isolates the Pt/Pd print from harmful gasses, especially the sulphurdioxide (SO2) that may be catalyzed by Platinum to harmful sulphuric acid.

    Luckily, SO2 emissions have gone down considerably over the past 20 years or so in the West (see my previous post above), meaning current conditions are unlike the Victorian industrial age smog ridden cities (or as recent as 1952 London), where many of the most severely affected Pt/Pd prints might date from. Still, we are not down to pre-industrial age clean air, and situations in some parts of the world are undoubtedly still bad.

    - Print 100% Palladium prints. This is only a partial solution, but since Palladium seems not to facilitate the catalyst conversion of SO2 to sulphuric acid, you will have reduced the chances of serious acidification as per described issue 1), although this is by no means a guarantee that no acidification at all will take place in the very long run, just that it will be much slower. CalciumCarbonate containing papers will reduce ill effects as well, by providing an alkaline buffer.

    - Employ the best clearing and washing techniques. Clearing in Pt/Pd printing, but also other Iron based processes like VanDyke Brown, removes the Iron sensitizer after exposure. This is a vital step in the processing of Pt/Pd prints, especially for the long term survival of the print. Any retained Iron in the print may cause harm, although full removal of all iron is probably impossible (see remarks above), but safe levels are obtainable.

    A good recommendation is the process described by Mike Ware in this article:

    Chemicals required for the Processing Solutions
    • Ethylenediaminetetraacetic acid disodium salt, Na2Edta (pH 3-4)
    • Ethylenediaminetetraacetic acid tetrasodium salt, Na4Edta (pH 9)
    • Kodak 'Hypoclear' powder or sodium metabisulphite or sulphite

    1 Disodium Edta (5% w/v) 10 mins
    2 Rinse in water half min
    3 Kodak Hypo Clearing Agent (working) 10 mins
    4 Rinse in water half min
    5 Tetrasodium Edta(5% w/v) 10 mins
    6 Wash in running water minimum 30 mins

    Please note though:

    * It is of vital importance to wash out all EDTA in the final washing cycle. EDTA is what is called a "chelating agent", it binds with the Iron (both Fe2+ and Fe3+) as present in the sensitizers, and forms rather soluble complexes that can be washed out. However, EDTA-Iron complexes, can still induce Hydroxyl radical formation as described in issue 2), and hence may still cause damage if left in the paper. It is therefore vital to properly wash the prints and remove all complexed Iron/EDTA.

    * All chelators like EDTA, and the in paper conservation world used Calcium- or MagnesiumPhytate chelators, preferentially complex with Fe2+. In addition, Fe3+ can form some less soluble compounds compared to Fe2+ and probably binds to the cellulose fibres. See remark below by Mike Ware regarding Fe3+ cations and it's lesser solubility compared to Fe2+:

    "That may be because it's quite strongly bound to the cellulose via vicinal -OH groups, - or if Fe(III) hydrolysis has proceeded very far (a complex process) it may be macromolecular "hydrated ferric oxide" physically trapped in the cellulose microfibrils. Eventually it turns into the highly insoluble mineral, Goethite FeO(OH). Any, all, or none of these hypotheses may be correct!"

    This all means that if any Iron is left in the print after proper clearing and washing, it is most likely Fe3+ species.

    - To ensure proper removal of Fe3+ a SodiumDithionite/EDTA bath might used. SodiumDithionite is a reducing agent with a neutral pH, that will convert any Fe3+ to Fe2+, allowing it to be more easily washed out together with the EDTA (See "A Conservation Treatment to Remove Residual Iron from Platinum Prints", and the short reference to the function of SodiumDithionite on the Ink Corrosion website here).

    - Use Bathophenanthroline Indicator Paper for testing for remaining Fe2+ (will not detect Fe3+) 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 the page here.

    The usage of Bathophenanthroline Indicator Paper is described in this PDF document on the Iron Gall Ink Corrosion website.

    They can be bought at: http://www.preservationequipment.com called "Iron Gall Ink Test Paper":
    http://www.preservationequipment.com...Ink-Test-Paper

    This test could serve as a Pt/Pd equivalent of a "residual-silver" test as employed by traditional silver gelatine printers for testing of adequate fixing of silverhalides from silver gelatine papers.

    NOTE1: Since the test strips only detect free Fe2+ cations, not free Fe3+, use of a SodiumDithionite bath as described before might be good to ensure as much as possible conversion of the Fe3+ to Fe2+ cations, although according to Mike Ware in this article, the SodiumSulphite or Hypo Clearing Agent, will serve to this purpose as well, although maybe not as effective as SodiumDithionite:

    "Clearing of the residual iron compounds from the paper is improved by immersion next in a bath of Kodak Hypoclearing Agent interposed between the two Edta baths; alternatively a solution of sodium sulphite can be used. The inorganic sulphite in this tends to reduce any residual iron(III) to iron(II) which is then removed in the final tetrasodium Edta bath; the advantage is that these last two baths have a high pH (ca. 9) which is optimum for complexation of iron(II) and leaves the paper in a beneficial alkaline condition. The wet-processing sequence is summarised below."

    NOTE2: Bathophenanthroline Indicator Paper may also be of use to other iron-based alternative processes, like VanDyke Brown, for the same purpose.

    - There may be a small case for a CalciumPhytate or MagnesiumPhytate treatment as an alternative to EDTA, or as for example the second bath after a first EDTA clearing bath. CalciumPhytate and MagnesiumPhytate have been used in the paper conservator world (See here for CalciumPhytate or here for MagnesiumPhytate) to remove free destructive Iron from Iron Gall ink written documents. Both leave, when properly executed, the paper at very favourable pH of about neutral, and the working solutions themselves are close to neutral. In addition, Iron/Phytate complexes seem to be almost inert, meaning any complex left in the paper, is pretty harmless. On the contrary of all this, the treatment with Phytate may be a bit more laborious, and Iron/Phytate may be less soluble and hence more difficult to wash out compared to Iron/EDTA complexes.

    Detailed instructions for preparing and using CalciumPhytate can be found on the Ink Corrosion website.

    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

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  2. #2
    df cardwell's Avatar
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    Nice. Thanks.
    "One of the painful things about our time is that those who feel certainty are stupid,
    and those with any imagination and understanding are filled with doubt and indecision"

    -Bertrand Russell

  3. #3
    Bob Carnie's Avatar
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    I concur with Mr Cardwell
    very helpful informatin
    Quote Originally Posted by df cardwell View Post
    Nice. Thanks.

  4. #4
    Vaughn's Avatar
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    Thank you, Marko.

    May I copy this and use it in workshops and give it to our university students? (with a credit line to you, of course.)

    Vaughn
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  5. #5
    Marco B's Avatar
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    Quote Originally Posted by Vaughn View Post
    Thank you, Marko.

    May I copy this and use it in workshops and give it to our university students? (with a credit line to you, of course.)

    Vaughn
    Yes, no problem, it is all publicly available knowledge and articles I refer to. You might want to credit Mike Ware for his kind remarks as well, although I think I have already done that more or less properly in here.

    Also remember that most of the discussed issues, are equally valid for any of the other Iron based process, like VanDyke Brown.
    Last edited by Marco B; 06-10-2010 at 10:18 AM. Click to view previous post history.
    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. #6
    Marco B's Avatar
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    Important CORRECTIONS to my conclusions

    Hi all,

    Mike Ware was kind enough to give some remarks on my last set of conclusions.

    Especially noteworthy of course the remark about papers having an alkaline CalciumCarbonate buffer. While they may be good from a point of longevity of the paper base, as Mike points out, they are "disastrous" for the iron sensitizer itself, making it difficult if impossible to get good prints at all in the iron based processes, so this topic should be skipped.

    Of course there may be a case for an alkaline Calcium(Bi-?)carbonate bath after the print has been completely processed to restore a slightly alkaline buffer (as is mentioned on the linked Iron Corrosion website), but that is a different story...

    Upon my request, he has also given some more information on the possible use of SodiumDithionite/EDTA bath and how to employ it.

    Many thanks to Mike Ware for these further comments.

    *** Mike Ware's comments ***

    Sodium dithionite becomes a much more powerful reducing agent in alkaline solution.
    Sodium dithionite is unstable in acidic solution, decomposing to thiosulphate and bisulphite.
    The complex formation between Fe(II) and EDTA is a maximum in alkali (~pH 10).

    So to get the best reduction of Fe(III) to Fe(II) and removal of Fe(II) as chelate, one must therefore use alkaline solution.
    That means, effectively, using Na4EDTA not Na2EDTA.
    Rees and Gent started by using Na2EDTA (possibly, they didn't have any Na4EDTA) and adjusted the pH by addition of NaOH. They found rather little iron-removal action at pH 6.5 and much more at pH 8.5. (I won't go into the additional conservation reasons why they tried the lower pH).

    My present recommendation is simple:

    A solution that is 2.5% in Sodium Dithionite and 2.5% in Tetrasodium EDTA, which should result in a suitable pH around 8.5, with no need for adjustment.
    Treat for half to one hour. Stronger solutions could be used, but this is economic and effective, and should be frequently changed, if one is treating a lot of work.

    If you are editing your article, could I just point out a couple of things?

    The word you need in the intro paragraph is "threat" not "thread".

    In 1) NOTE: the absence of catalytic activity with palladium is NOT PROVEN so far as I know. I have just not seen any evidence of it, that is all. Absence of evidence is not evidence of absence.

    In -Print 100% Palladium prints : the recommendation of calcium carbonate containing papers is disastrous for all the iron-based processes because it promotes hydrolysis of the iron(III) photosensitizer. This advice completely defeats the original purpose! If you practiced any of these processes, you would know to pre-treat your paper with acid to DESTROY any calcium carbonate. Talk to Loris about this. I only use papers guaranteed not to contain calcium carbonate.

    ************************
    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?"

  7. #7
    Marco B's Avatar
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    LATEST VERSION OF ARTICLE

    Hi all,

    I have now updated and rewritten my set of conclusions on the longevity of Platinum / Palladium prints. It is now a more accessible and complete "article", with a proper introduction and a few more pieces of background.

    There have been a number of significant changes, and I therefore consider the above posts OBSOLETE.

    Please download the latest version that I attached here if you would like to read it.

    Marco
    Attached Files
    Last edited by Marco B; 06-16-2010 at 03:18 AM. Click to view previous post history.
    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?"

  8. #8
    clay's Avatar
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    Excellent resource. Thanks!
    I just want to feel nostalgic like I used to.


    http://www.clayharmon.net - turnip extraordinaire

  9. #9

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    Marco, I'm getting ready to learn to print pt/pd and other methods; reading things like this let me know that there is a lot more for me to learn. It's interesting though. I can't say I have absorbed it by any means, but will be something I reference again, and again. Thanks much.
    Tim Flynn



 

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