Uneven development with Caffenol

Attached is one frame from a roll of 120 (happened to be Adox ORT 25, but I've seen similar effects with other films in Caffenol, now and again) with a bit of a problem: The centre is less developed than the edges. (Note that this is from a TLR, so the "sides" of the image were at top and bottom in the tank.)

Development details: Caffenol LC+C, something like 14 minutes with 10 inversions every 3 minutes. The tank has a top and bottom, so it was always sitting in the same orientation between inversions, which is one of the things that puzzles me---if the gradient went from one edge to the other, I'd think that the developer was incompletely mixed and some crucial component either settled or rose, but how would the problem occur on *both* edges?

Too much agitation, not enough agitation, incomplete dissolution of something...? I'm open to suggestions.

(The original is at <http://www.flickr.com/photos/ntenny/2552113596>, if you want a closer look.)

Thanks

-NT

Probably an agitation effect. Every three minutes is probably not enough, particularly with this kind of weak staining developer. Normal agitation for PMK, for instance, is every 15 sec., which is what I'd use with caffenol in a daylight tank.

I find with this process that I need agitation little and often say 2-3 inversions every 30 seconds followed by a sharp tap.
Also I like to develop for 30 mins, I know it sounds excessive but the dev is weak.
Possibly its more pronounced in certain areas as its 120 film and the centre is touching or close to the emulsion of previous frames.
Mark

The flow over an edge is often of higher velocity, which might cause higher density & contrast in the edge of a reel. The "gentle" inversion method might cause it, especially on the wider films. You could try vertical shaking with small movement amplitude and no inversion. Rapid small amplitude changes in flow direction can produce the necessary mixing with a smaller edge-to-edge velocity gradient. Needless to say, test before serious use.

When I've seen this before it has always been due to agitation. And I have seen it, using more conventional developers; I'm sure it has nothing to do with the espresso. I suspect that Patrick is on to the cause of it in the post preceding this one. That is the first thing that came to mind; quiet agitation with periodic activity during which the flow over the coils in the reel creating turbulence which produces greater exchange of fluid into the emulsion.

I'd recommend the most ordinary agitation possible. You know, 20 seconds to begin with, then 5 seconds every minute with taps following the cycles, especially the early ones to dislodge air bubbles. But then, I'm a curmudgeon.

Of course, if all else fails, total is total. Violent agitation throughout the whole time (which would have to be shortened) would certainly work. But you'd get tired.

Are you sure this is happening in dev, and not just negative curl in the scanner? Have you tried a contact print under heavy glass to make sure the neg is flat?

I see this with 35mm, and it's usually just because of humidity or other factors leaving a bit of curl to the neg.

Scanners I have used seem to have a fairly high depth of field. You could test it by scanning the film both with emulsion toward the scanner and the opposite You might be surprised at how little diference there is, even with a glass plate negative.

KD5NRH said:

Are you sure this is happening in dev, and not just negative curl in the scanner?

Click to expand...

Yeah, it's definitely there in the negative.

Thanks for the agitation advice, everyone---I'll try slight-and-frequent next time. I've also seen people talk about adding a restrainer to developers with a tendency to fogging and unevenness, and I may try that as well just to see what happens.

-NT

ntenny said:

Yeah, it's definitely there in the negative.

Thanks for the agitation advice, everyone---I'll try slight-and-frequent next time. I've also seen people talk about adding a restrainer to developers with a tendency to fogging and unevenness, and I may try that as well just to see what happens.

-NT

Click to expand...

You are welcome.

Fogging - that would perhaps be appropriate. Unevenness? I doubt it.