Does the coated Pt/Pd emulsion become weaker if left to dry too long before exposure?

[largo]

Hello!
Happy New Year to all!

(Newbie here on this forum, but not a newbie concerning alt processes

Yesterday I made a Palladium A4 print with the following features / consumables :

- A good digital negative on Pictorico OHP Premium transparent
- Bergger COT 320 paper
- 24 drops of Ferric Oxalate
- 24 drops of Sodium Chloropalladite
- Coating with a spalter brush
- 16 minutes of exposure under my UV lamp.
- Development in Ammonium Citrate at 20°C
- Clearing in 3 baths, buffering, rinsing etc etc ...

In brief, the same protocol (DOP process, not POP) and consumables that I have been using for a year for Palladium prints ...
But I was quite disappointed by the result this time, which I found not contrasted enough, too greyish. The highlights are correct, but the midtones are too dark / muddy and the shadows are paradoxically not dense/black enough. So a general lack of contrast...

Last night I couldn't find the cause of this change in the print result, all the "variables" having remained the same with my previous prints... Then, I remembered this morning that when I removed the exposed paper from the contact frame, I found the image already very visible, to my great surprise, whereas usually you can barely guess it after exposure, and it appears entirely when the developer is poured. Yesterday when I poured the developer, the midtones darkened, but the shadows already very visible did not really darkened (I have a video showing the print after exposure and before development and the effets of the poured developper)...

It remained to be understood why the image had become more visible than usual during exposure... ? And here I see a possible explanation : After sensitizing the paper, I let it dry only 60 minutes, because it was already dry after 60 minutes, and because I read in this source http://www.jeffreydmathias.com/assets/chapter7.pdf , page 17 :

Notes:
- Coating must be "bone dry" for exposing.
- Coated paper might be stored for up to an hour. Dry once again immediately prior to exposing. Never store for longer than an hour. The coating will depreciate with time; so, no matter how it is stored, it will go bad.​

So I followed this recommendation not to let the paper dry for more than an hour, but I also made sure it was absolutely dry before exposure (DOP process, not POP/malde-ware as a reminder) . While I usually let the paper dry for more than 24 hours...

And I have the feeling that this could explain why the image appeared much more after exposure and before development than usual: my reference exposure time of 16 minutes became way too long for this fresher and more sensitive emulsion ... Hence:
- I think shadows suffered from solarization
- middle tones became too dark (overexposed)
- but the highlights remained white because the negative blocks UVs well for these areas no matter how long is the exposure time ...

What do you think about it ? Do you agree with Jeffrey Mathias ? Have you also observed that a too long drying time of the emulsion makes it "weaker" ?

If yes, it means that
1) this drying time/condition becomes a new variable to take into account for the calibration of our procedures (exposure time, etc...), and
2) that I am surprised to have read this in only one source (mentioned above), although I've read a lot of literature about Pt/Pd prints... ?

Thanks for your feedback and tips !

Loïc

 

[Alan9940]

I use a different mixture, but I’ve left coated paper overnight and never noticed any difference. Are you sure the FO is good? Shelf life is only about 6 months.

 

[Vaughn]

Prints made with only palladium run the risk of solarization with long exposures -- the blacks start to reverse and get lighter.

 

[largo]

My ferric oxalate is 3 months old. (I bought a 27% solution online). I kept it in the fridge during the first 2 months, I've been told it can even be kept frozen...
I actually did another test with a shorter exposure time and indeed the results are not satisfying. So my hypothesis was wrong. An issue with my FO is possible...
Could a couple of H2O2 drops save my FO ?

 

[Alan9940]

Personally, I wouldn't try to save it, especially if I thought it might be an issue. But, I mix my own to ensure I'm always working with fresh solution.

 

[nmp]

My ferric oxalate is 3 months old. (I bought a 27% solution online). I kept it in the fridge during the first 2 months, I've been told it can even be kept frozen...
I actually did another test with a shorter exposure time and indeed the results are not satisfying. So my hypothesis was wrong. An issue with my FO is possible...
Could a couple of H2O2 drops save my FO ?

If the FO was compromised (reduced to ferrous,) I doubt if you would have had clean whites. You can check by doing a K ferricyanide test. If it turns blue, it got reduced somehow. Usually they last much longer than 3 months if stored properly.

 

[Ian Leake]

Two quick thoughts: when ferric oxalate gets old, you can get weaker prints. This is easy to test as a root cause by mixing fresh ferric oxalate.

Historical sources all stress the need for bone dry sensitiser. This is an oddity, because with modern materials it is clear that slightly damp sensitiser produces much stronger blacks. Ideally the sensitiser should be just dry enough not to stick to your negative (you can keep your negative safe with a sheet of transparent material between it and the sensitiser. I use rubylith backing sheet.) One theory is that the ‘bone dry’ recommendation came about because sensitised paper was usually made in batches for storage and that the paper stock usually contained gelatin which is bad for platinum.