August 1, 2010

uneven development

 click on the picture for bigger size

 Some people report uneven development and/or disturbing fog. That effect appears almost always with classic (cubic crystals) emusions like Ilford PanF+ or Agfa APX 100. Not enough agitation is the cause. A drastic example is stand development with Caffenol-C, as you can see in the image above.

What is happening? Lets regard the left picture. Stand development makes it visible. Classic bw-emulsions contain a lot of silver-bromide, the silver is reduced by the developer to form the blacks, and the bromide is set free. Bromide is a strong restrainer, but without or too less agitation it sinks down in the tank and produces less development, marked with a red "x" in the left picture.Also below parts of high exposure more bromide is set free and causes streaks. Below the sprocket holes, less bromide is set free leading to stronger development. Finally the bromide accumulates at the bottom and there we find the least development and - the least fog!

In the right picture with regular agitation we see no eneven development or fog at all exept for the small upper and lower parts covered by the reel during development. The bromide is dispersed evenly and so we have a constant restraing effect over the whole area. The uncovered upper and lower borders are developed evenly  with low fog level, see the red "x"-es.

So agitation is the key for even development. Of course there is some remaining general fog,  but doesn't disturb because it is spread evenly over the whole film. If you get uneven development or disturbing fog, agitate more! Try the heavy agitation regime recommended f.e. for Xtol, 5 times in 5 seconds every 30 seconds. That's almost shaking! And reduce dev time when doing this! Time, temperature and agitation are closely related, keep that in mind always.

My trial with stand development was very revealing. It was done when experimenting with low-pH Caffenol-C. As the development times with low-pH will increase and I didn't want to shake the tank for 20 or 30 minutes, I gave stand development a try. With the shown faults. But - when adding the bromide in a good amount from the beginning as a separate agent, unevenness and fog will be gone! So stay tuned and await a new Caffenol-developer by me, it will be named Caffenol-C-L. Only a little bit of fine tuning necessary.  Compared to C-C-M it will have a bit film speed loss, but probably still boxspeed, finer grain and fog free even with stand development!

With "modern" medium speed films like Acros100 or Tmax100 things are different. They contain much less bromide and are much less fog sensitive and show perfect even development with C-C-M. Maybe C-C-L will also be recommended for high-speed films. So some things to do in the future, it doesn't get boring at all.

Time for a cup of coffee - cheers - Reinhold

5 comments:

K Matthias said...

Reinhold, there might a middle ground without adding bromide. Intermittent agitation during the stand time. I found pretty good results doing that with Rodinal after having similar results to yours. Also 120 film without sprocket holes exhibits less streaking.

imagesfrugales said...

Oops, here's the "second comment". No, you will have some bromide streaking, the sprocket holes are not the not the cause but not enough agitation. The APX is the most sensitive film in this respect that I used so far, with modern emulsions it may work better.

Cheers - Reinhold

Andy said...

Dear Reinhold:
Thanks for your work on this. My first 2 rolls of 120 Acros 100, souped @ 20C per your original CCM directives, were afflicted with UNDERdeveloped edges, it seems: Dark bands on the positives, heavier on one edge than the other. (I'm new to scanning, I admit.)
Do you think more agitation per DenverDad is the solution? Or KBr?
Schone grusse aus Kansas.
-- Andy

imagesfrugales said...

Hi Andy,

usually the upper border of the neg is overdeveloped like it can be seen here. Denvderdad had the same probs with sheet film. Here's not the best place for detailed discussions, you should post your question at Apug: http://www.apug.org/forums/forum37/ and add a link for a sample picture.

Best - Reinhold

Andy said...

Thanks, Reinhold. I'll do that.

-- Andy