Clearing PtPd/Residual Staining/Library of Congress Video

https://www.loc.gov/today/cyberlc/feature_wdesc.php?rec=7225

Link above is to a video. A pair of Library of Congress archivists did extensive tests on Iron/Noble metal prints and found that it was very difficult (maybe not practically possible) to totally eliminate Fe2 and/or Fe3 in paper. This contamination ultimately led to yellow staining of one degree or another. They tried EDTA, DPTA, combined with Sodium Dithionite, and concluded that even with very careful processing, PtPd and other iron processes were basically impossible to clear.

I'm getting back into this after many years away. Found a great UV box, working on gathering everything else, but wondering if people who do successful PtPd have noticed staining of prints. I've been examining prints that were "clear" in 2006 that really look like crap now.

Watch the video if interested and share your thoughts on archival clearing. Thanks,
Neal in NJ

The same author, Dr. Matthew L. Clarke, has contributed a chapter to Platinum and Palladium Photographs, Ed. C. McCabe, (Washington DC: American Institute of Conservation, 2017) which shows that effectively complete clearing of Fe can be achieved with the right procedure. See pp.108-110: "This 3-step bath is therefore highly recommended regardless of the paper support or sensitizer employed, as it consistently and efficiently reduced the residual iron."
See also my Platinomicon, §10.10, pp.221-2.
N.B. Anyone intending to write about this topic must specify which basicity of "EDTA" they are referring to. There are 5 possibilities.

This is really interesting, thank you for providing such interesting material.

I am wondering if this can be applied to other siderotype prints, especially cyanotype prints.

What would be the “best” or the most effective way to really clear a siderotype print?

Working with cyanotype, I have seen some extensively washed prints’ highlights change after some time.
So what would the most adequate steps and the right chemistry be to effectively reduce residual iron?

Many thanks.

Mike, just so I’m clear, you’re suggesting that in order to participate in the discussion you have to state your EDTA recipe?
Could you just help me get to the punchline? What works?
Thanks
Neal

Neal-

I have prints that I made 15 years ago that are not showing any appreciable staining. They may not be 100% clear, but they're clear enough.

I too have a lot of old prints. I committed myself to PT/PD in 1987 or so. For the most part my collection of my own prints has been kept in boxes and rarely seen the light of day. The vast majority are good as new but occasionally I run across a print with a speck that is yellowish or orangeish.
I have found that if I let my prints stay in the developer a full minute or two they clear much more quickly. In the beginning I bought into the idea that platinum prints develop instantly and I would only leave them in the developer for 15 seconds or so. I had a lot more difficult time in those days getting my prints to clear.

I've had a framed (under regular window glass) pt/pd print hanging in my home for, at least, 30 years and it certainly could be very slowly changing before my eyes, but it looks the same to me now as the day I bought it. Being that it is by another photographer, I have no idea of how it was processed. In my own pt/pd printing, I use 3 EDTA clearing baths and, though my oldest print is only several years old I haven't noticed any changes.

EDTA formula:

1 tbsp EDTA
1 tbsp Citric Acid
1 tbsp Sodium Sulfite
to 1L water

I remember I had lots of trouble with clearing in general. I did get some prints that LOOKED clear, but those now look tinted after 12 years of storage. My issues with hard to clear prints all those years ago might have been related to anything--paper (I was using mostly some paper from Legion that was popular at the time), humidity, my water (slightly hard, but not crazy hard). I tried EDTA and Citric. I don't remember ever playing with Dithionite. I also never tested Ph, so I have no way of knowing the basicity of my EDTA. I am hoping to start over with a process that eliminates as many variables as possible.

Neal - in response to your - very reasonable - request for clarification: "EDTA" is short for ethylenediaminetetraacetic acid. As its name implies it is a tetra-basic acid with four replaceable hydrogen ions. So it's clearer if we abbreviate this free acid as H4EDTA. But this is not the substance any of us use. There are four possible sodium salts of this acid: NaH3EDTA ; Na2H2EDTA ; Na3HEDTA; Na4EDTA. Of these, the so called "EDTA" of many recipes and commercially supplied kits is actually tetrasodium EDTA, Na4EDTA, which gives a distinctly alkaline solution, pH ~9, which can hydrolyse iron, Fe(III), rather than chelating and removing it effectively, and ultimately cause brown staining. I have always advocated using disodium EDTA, Na2H2EDTA, in the first clearing bath, which is still acidic, pH ~4, and cleanly removes most of the Fe(III), without any hydrolysis. For the second clearing bath, I recommend a reducing agent, sodium sulphite, to reduce the Fe(III) to Fe(II), which is less strongly bound to the cellulose, and then this residual Fe(II) can be efficiently removed by the third clearing bath of Na4EDTA, which leaves the paper sheet in a healthy alkaline condition. For further explanation and detailed procedures see my recommended texts.

Thanks Mike. Your resources were helpful. I'll give those clearing steps a try.