fog and stain... aka, clearing Pd prints in situations with alkaline tap water


I’ve been tracking down the source of density in the highlights of recent calibrations and after ruling out chemical fog, finding a bit of UV induced density, I found that the culprit is my very alkaline tap water. As in pH 9.6 (reported; I’ll test very soon).

During some this weekend and reading at APUG and I suspected my tap water could be driving this. On a whim I tossed some vinegar in the first clearing bath. Viola. It didn’t completely clear I suspect because the stain was set in during a two minute wash of warm tap water after development.

My emulsion is Pd with a drop (or two) of Na2, developer is potassium oxalate. Paper is Hahnemuhle Platinum Rag. Clearing baths are mix EDTA and a Permawash.

I am certain this is a main driver of the stain (not fog) but am not 100% of the workflow to solve it. By next weekend I should have this all sorted and will report back


Here’s the latest.

At the end of the week, I received some chemistry ordered last weekend and over the last couple of days I picked things up again. Procured this week were: citric acid, oxalic acid, sodium sulfite, and a replenishment of EDTA tetrasodium. I wanted to mix a new clearing bath recipe (Keith’s), a dilution of citric acid for the first bath, and oxalic acid dilution for keeping the developer (Potassium Oxalate) on the acidic side of the fence. Oh, and one more thing; I order some full-range pH tips.

First thing I tested was the pH of tap water. It’s right at 7, not the reported 9.5. That make a lot of sense on one hand but tosses my hypothesis that my problem was alkaline tap water right in the trash bin. Next, test the pH of my developer; it read 7. Interesting.

I won’t bore you with all the iterations of clearing baths, washing after developer (or not), etc, but here is what I have found. My best results for clearing use the following: developer, 5 min wash in warm tap water, 5 min citric acid, 5 min clear, 5 min clear.

Keeping the pH of the developer acidic seems to be a key.

I am still not getting “paper white”. The visual density measures the same (0.03) but when you look at the CMY number a 0.01 increase in yellow is measurable. This can just barely be seen too. I’m thinking this might be related to the 64%ish humidity of my coating environment. I’ll continue to work to sort that out, but I think my environment is stable enough to proceed with calibration.

More as it develops.

Pun intended.



Hi Scott,

Glad you are making some progress. What stands out to me in this story is what you said about there being no increase in visual density at step 1, but a tinge of yellow. This suggests that your issue is not fog, which would be gray, but stain - in other words, insufficient clearing.

I may have mentioned this in our private conversation, but have you tried eliminating the pre-wash between developer and 1st clear? I used to do this too a long time ago, but eliminated it for some reason I don’t remember. Try it if you haven’t already.

Also, add oxalic acid to your developer to bring the pH down to around 6.5.

Thanks for the report.


Keith you are spot-on on all factors.

I did test using the post development wash before going to the citric acid bath, and without. I found no negative stain caused by that wash. Things do seem to clear faster using the wash before the citric acid and require less time in the subsequent baths. I have one more test to conduct tonight but I think I have data showing a loss of print density when staying in the clearing washes too long. I’ll report back on that tomorrow.

Regarding the oxalic acid, I think keeping the developer slightly acidic is critical in my setup.

Overall my problem is definitely stain, but in the course of all this testing I tried a couple of different LED light sources in my coating room and did find that it is possible to fog with LED light sources. Needless to say, that source is no longer in service for these purposes.


Hi Scott

I agree with Keith about developer pH, and hope my thoughts about the post-development process help with the highlights not clearing. (With the developer, use distilled water instead of faucet water.)

Follow development with a fresh water rinse (distilled may be better considering the alkalinity of your mains supply). Then…

  1. EDTA disodium salt (~ 50g + 1 liter water), 10 minutes [exhaustion: use until yellow-brown]

  2. freshwater rinse, 1 minute

  3. Sodium metabisulfite (hypo clearing agent, ~ 25g + 1 liter water), 15 minutes (greater concentration is not critical) [exhaustion: use until very light yellow]

  4. freshwater rinse, 1 minute

  5. EDTA tetrasodium salt (~ 50g + 1 liter water), 15 minutes [exhaustion: use it begins to discolor]

  6. freshwater rinse, 1 minute

  7. Wash 20-30 min

These steps should ensure a very through removal of any deeply residual iron compounds, which may be the most likely source of the uncleared highlights. I good way to visually test for this, of course, is to block out with rubylith or other UV opaque material a section of your coated area adjacent to an uncoated area.

It is important to use the two EDTA salts in the above sequence. Each does something different by way of removing the iron compounds, and reversing or avoiding the EDTA disodium salt significantly affects clearing.

All of this said, I am have not tested clearing with your particular paper + sensitizer + developer combination so my suggestion may not be at all helpful! Finally, it is hard to find disodium EDTA at short notice. I’d be glad to send you a small packet if you want.

Hope this helps!


Good to see you here Pradip! That is an interesting clearing routine. I wonder if your ammonium ferric oxalate print-out system is more difficult to clear than the traditional ferric oxalate system. The only time I remember ever having a problem with clearing was back in the mid-90s when I first tried Arches Platine. That was when I learned about using Kodak Hypo Clear (mostly sodium sulfite and metabisulfite) as a clearing bath for Pt/Pd.

For the last 15 years or so I have used a mixture of tetrasodium EDTA, citric acid, and sodium sulfite (dissolved in that order) in 3 consecutive baths. It has never failed me. I was going to track down some disodium EDTA long ago when I first came across the articles you wrote with Mike Ware, but never got around to it. A chemist told me that the citric acid converts the tetrasodium EDTA to the disodium form. Do you know if that is true?



Thanks Keith, and glad to be here! :slight_smile:

I am not sure about whether the ammonium system is more or less difficult to clear than potassium-based or other formulae. So much depends on other variables such as paper, developer, and even, as Scott points out, on the water supply. I share your concern that the matter of clearing residual iron compounds is important to all variations of pt/pd processes.

I was lucky enough to work with Mike Ware and a number of conservation scientists at the Smithsonian and other national museums a couple of years ago, whose findings are about to be published in a large volume about platinum and palladium printing (I’ll be sure to post more details as soon as we have a publication date). Much of their work around residual iron in pt/pd prints may be summed up as follows.

The presence of iron compounds in paper fibers can lead to deterioration. The presence of iron compounds in prints can induce overall or localized print discoloration. Thus, for archival and aesthetic reasons, it is desirable to process pt/pd prints in such a way as to keep iron content to a minimum.

The team tested many formulae and combinations for clearing platinum, palladium and platinum-palladium (1:1 by sensitizer volume) with potassium and ammonium-based systems, development-up and print-out, on a number of different samples of the most suitable papers. It then ran all the prints through standardized simulated aging tests.

What we concluded was that the most efficient clearing sequence, regardless of sensitizer formula and development method, was the one of Disodium EDTA first, then hypo clearing agent / sodium metabisulfite, then Tetrasodium EDTA, using the strengths and times, with interspersed rinses, that I describe above. What is important is that this applies to whether or not one uses a developer prior to clearing, and that the sequence makes a big difference.

Another thing to note is that while many of the tests looked just fine after washing and drying, the aging tests began to display visual changes in clearing methods that did not use disodium EDTA first.

So, even if tetrasodium EDTA is somehow converted to disodium in the presence of citric acid (I don’t have enough expertise to comment on this, but will look into it!) it is not happening when disodium EDTA is most needed… at the first instance after development in development methods, or at the first instance of processing in print-out methods.

It does not take much to add the disodium EDTA to your work flow and is well worth the extra few minutes. Besides, it makes the final wash much more efficient and if water temps are kept close to process temperature, the final wash may be reduced to the minimum 20 minutes, thus saving water, and reducing paper swelling.

I hope this helps, and remain eager to know if Scott finds a solution to his problem!

I had similar problems to your about clearing Arches Platine, years ago. But this new batch, which became available last year, is wonderful. It clears without any problem, and to add to this, the paper is strong, renders astonishing dMax, coats well (I use a glass rod), and has, most important, a grain-free rendering of mid-tones and highlights. I am also managing to get a lovely range of tones going all the way to blue-black at the higher hydrations ( pt:pd at 1:1, ammonium system), but have heard from other printer friends that the potassium chemistry renders a very warm black only.

I’ll post an image in a few days of an Arches plating print.


important error correction:

Another thing to note is that while many of the tests looked just fine after washing and drying, the aging tests began to display visual changes in some clearing methods that did not use disodium EDTA first.”


There was a conference a few years ago about this, right? I really wanted to go but couldn’t for some reason I no longer remember. I look forward to the publication.

Dick Arentz was my teacher (and I was later his workshop and research assistant) when I got started in Pt/Pd in 1991. His preferred clearing bath was phosphoric acid in 3 consecutive baths. At that time Bostick & Sullivan was recommending tetrasodium EDTA alone for clearing (I think they still do, at least that is what comes in their kits, which is part of why I don’t recommend that students buy the kits), and some printers (George Tice and a few others) were recommending HCl. We knew that tetrasodium EDTA alone did a rather poor job or clearing, and I wasn’t keen on the idea of HCl corroding the metal objects in my darkroom, so I used phosphoric acid for my first 4 years of Pt/Pd printing. I think it was 1995 when I had the problem with Platine. I switched to using Kodak HCA for a year or 2 then began mixing my own from EDTA and sodium sulfite. Not long after that I picked up the idea of adding citric acid to the mix, and have stayed with that ever since. 1 tablespoon each per liter. I have seen a few clearing protocols with 3 baths of different composition, but never a good explanation of why that might be better. It does make sense that when working this way a water rinse between steps would help to prevent one bath from contaminating the next.

I’ll be very interested in the results of those accelerated aging tests. Back in the 1990s I worked at CCP in Tucson. They have a pretty good collection of Pt/Pd prints, both contemporary and vintage. I was very familiar with them. The only ones that I remember having conservation issues were some early Paul Stand prints that had become quite orange in the highlights. I think it’s a safe guess that this is from insufficient clearing. None of the other early works, and none of the later works that I can recall, had any signs of deterioration other than the paper becoming brittle in a few cases. This included works by Emerson, White, Weston, Kasebier, Anderson, Gilpin, and many others. Of course, back then they didn’t have an in-house conservator who might have identified some of the less obvious issues. Now they do have a full-time conservator, and the darkroom where I used to spend most of my time making reproduction prints for publication (this was before digital!) has been replaced with a state-of-the-art conservation lab.

Sorry for rambling! Maybe this isn’t the best place for an extended conversation about tangential topics. Gotta get back to the darkroom now.

Cheers -


No need to apologize and certainly not a ramble. These narratives and how they fold into our work are important. So glad to be part of the conversation.

Yes, much of the work I refer to was presented at conference in DC in October of 2014. It was a good gathering and fantastic for me as I got to meet some remarkable people.


Pradip, can I ask what pH value you have obtained with EDTA Disodium. Mike Ware has written that pH 3 to 4 is optimum for clearing, but I have never got lower than 5.5 with Disodium at any strength (using water at pH 7). I am not sure if this negates the advantage of Disodium over Tetrasodium.

I have experimented by adding Citric Acid to EDTA Disodium - it seems that only about 0.5 tbsp can be dissolved fully in 1 litre of Disodium but it will drop the pH to around 4.0. But, is this better than Disodium at pH5.5 or Tetrasodium with Citric Acid as Keith suggests?


Keith - I may have misunderstood your work flow. Sorry! I thought you have separate baths of tetrasodium EDTA and citric acid. But, if you do not, and are actually mixing the two to make up the first clearing bath in a sequence followed by sodium metabisulfite and tetra sodium EDTA, then you are golden (umm, I should say platinum :slight_smile: ). I have not done this or tested it, but Mike Ware suggests the following:

Citric acid 15g + tetrasodium EDTA 50g + water* to a final volume of 1 L

Kevin - (hello!) You should be fine. What is not recommended is having a first clearing bath with pH values higher than 7 ( tetrasodium EDTA leans towards pH10) and can eventually lead to yellow staining. It is important that the solutions are prepared with some degree of accuracy, and I prefer to dissolve the solids in very warm water.

I don’t think I have given you a clear set of responses, but hope the suggestion of using a disodium (or tetrasodium+citric acid) EDTA bath as a first clearing step helps! If the disodium EDTA* - Sodium metabisulfite - tetrasodium EDTA sequence renders prints that after drying look well cleared to the naked eye, you should be in good shape. If not, there are probably other reasons that are preventing effective clearing (sensitizer ingredients, paper, excessive hydration, developer).

*I always use distilled water for my first clearing bath, and at around 40C / 100F to thoroughly dissolve the solids. Let cool to room temp before using.


This 50 minute video puts this thread into perspective in regards to stain and aging…

Removing Residual Iron in Platinum and Palladium Prints



Thanks Jon, for posting the video! My friends and colleagues Matt and Dana did a great job of presenting, and summarizing many months of hard work. And, from their research, it is kind of alarming how vulnerable the pt-pd print is to the presence of iron in paper. Their work has certainly brought to the fore what has been a whispered conversation, up till recently, about the state of many of the most notable pt/pd prints in major collections. And collectors, as well as us pt/pd printing photographers, need to pay attention to the best practices suggested by the research.

It should be noted that Matt and Dana were concentrating on the conservation treatment of pt prints with undetermined processing histories. Their samples were intentionally ‘designed’ to have residual iron in them. While the conclusions are of importance to all of us, whether we are makers, collectors or conservators, the matter of processing a print as opposed to conserving a print has to be underscored in our discussion here. Matt and Dana’s work suggests that relationship between pH and chelation of iron (II) and (III), but did not include disodium EDTA in their study - another group, looking to establish best practices for printers, worked on that. That other group found that for processing a print after development, the disodium EDTA, at the lower pH values, removes greater amounts of iron (III) compounds. The sodium metabisulfite (they used sodium dithionite which effectively does the same) reduces remaining Iron (III) compounds to Iron (II) which are then more soluble in the final, higher pH tetra acetic EDTA.

Thanks everyone for bringing this into the forum here. I do feel it is an important matter, and the discussion can only serve to help us all make better and more enduring prints.

PS: Jon - Cannot tell you what an honor it feels like to be in contact with you! :slight_smile:


Pradip, the honor is ours! :slight_smile: This community is amazing me.


I agree. I’ve largely extricated myself from online discussion boards, through lack of time and a need to wallow in gentle ways. This ‘place’ though is focused, smart and supportive. Sharing is caring. I like that. Thank you!