Chemical Fog?

[ronlamarsh]

I just processed a batch of 4 4x5 sheets in D-23 1:1, arista edu ultra 400, exposed @ 200asa, for 13min. When I go the laights on after fixing I was dismayed to find that there seemed to be a very high B+F and even a mottling as if fogged. I processed a batch of HP5+ identically and no issues. I noticed this yesterday on a batch of 5x7 edu ultra 400 in d-23 1:1 but the same film from the same box shot on the same day processed in Ansco 47 beautiful? Is the EDU Ultra more sensitive to chemical fog? I used to process edu ultra 200 in D-23 all the time without issues.

 

[fschifano]

Well, I haven't noticed that with Arista.edu Ultra 400, though my experience with this film is all with miniature and medium format. Perhaps a bit more agitation would help, or perhaps a pre-soak. Sounds a bit like an overlooked processing error to me.

 

[Gerald C Koch]

Chemical fog rarely occurs but can be caused by two things:

1) The accidental introduction of some fogging agent to the developer. This can occur when reels and tanks are improperly washed.
2) Reduction of sodium sulfite to sodium sulfide. This can happen with replenished developers where bits of gelatine emulsion in the developer provide a nutrient supply for various molds and bacteria.

There is dichroic fog caused by silver being redeposited on the emulsion. This can happen with high solvent type developers. However it is very distinctive in appearance.