Fogging on PtPd prints

Hello All!

I have some very slight fogging apparent on my PtPd prints. That is, some tone remains after clearing in the print border, even when the sensitizer is covered with Rubylith film during exposure.


  1. It’s not the neg curve. The problem was first evident in the margins of my print, and so I assumed that the neg border was not dense enough. (ie a curve problem). I ruled this out by testing a print covered partly with Rubylith, which should prevent UV light transmission. The problem still persists.

  2. It’s not the darkroom. I have carried out exhaustive tests to see if there is a stray UV source in the darkroom. There is not.

  3. The problem is more apparent when the paper is wet. I am using Legion Revere. After the paper has dried down, the problem ALMOST disappears (but not quite).

Could it be that the sensitizer itself is fogged slightly? It is stored in a brown bottle in the darkroom, with the lid on whenever the darkroom door is opened. It does not receive UV light in the darkroom, but perhaps it could have happened before I received it.

Any other thoughts?


A few thoughts:

  1. Are you sure it’s fog and not stain? Fog can be from light or from sensitizer going bad. Stain is from insufficient clearing and usually has a very faint yellowish tinge.

  2. Has any part of your process changed between previous non-fogged prints and your current fogging problem? This includes new batch of paper, new sensitizer (either pre-mixed or not.)

  3. What chemistry are you using? DOP (ferric oxalate) or POP (ammonium ferric oxalate)? How old is it?

  4. What is your clearing sequence?

  5. What is your room lighting? There is a well-known alt-process supplier that uses fluorescent lighting in their darkroom. They don’t think it causes fogging, but after testing some paper in their darkroom several years ago, I can say as an absolute fact that it does. I brought my own chemicals (purchased from them) and used my then standard low contrast mix (DOP with a miniscule amount of Na2Pt as a restrainer). Under the fluorescent room light I got bad fogging though they swore they never got fog. Found a clamp on incandescent fixture, turned off the fluorescents, repeated the test and had no fog. Later I found out that they use a huge amount of Na2Pt in their standard mix for printing digital negs. The high level of restrainer is what they need to compensate for the fog produced by the fluorescent lighting.

More information is needed to help you diagnose the source of your fog problem. Please be as complete and specific as possible.


Dear Keith,

Thanks so much for reviewing this. I had to dig deep to review the process and make sure that I’m not making any obvious errors.

  1. Pretty sure it’s not stain. No trace of yellow. It’s a tone in about the 3-4% value and exactly the same color as the print color.
  2. No change in process, same paper batch, same senstizer, humidity etc.
  3. Using the POP method. Senstiser came from Jon at Inkjetmall and is less than 3 months old.
  4. Using a 3 bath clearing method as described by Pradip Malde. 10 mins in EDTA Disodiumj, 15mnins in sodium sulphite, and then 15 mins in EDTA Testra. Wash is 30 mins.
    I hear what you say about using Na2 to violently clear fog. It just masks the problem.

I got myself a UV light meter. My exposure is about 1700 “doses”. The lighting in my darkroom adds up to about 4-6 doses over 10 minutes (that is about the max time I have a coated sheet exposed to light in the room).

The other information is that the fog is very apparent when the paper is wet ( and therefore somewhat translucent). But the fog is easy to miss after the paper dries. I am using Revere 22x30 and I think it is 310 gsm.

Do you know if the brown bottles that store the chemistry are safe for UV light? Could the chemistry have gradually fogged in the bottle?


the chem is not going to fog in the bottle but you still want to keep it away from UV (keep it in a dark cool place).

But are your negs dense? Can you verify? I seem to remember this happening before and it was a neg problem,