agitation vs contrast

I just photographed a very important group of 22 with Foma 100 in strong sidelight and as luck would have it my fill light strobe failed. I was only able to make two exposures before the group disbanded. Panic stricken, I decided to develop the film one sheet at a time. I used Thornton's 2 bath developer and decided to try one sheet in a Unicolor print drum on a Uniroller with constant agitation and one sheet in my DuraLab paper slots, with very minimal 2 agitations in 5min in both baths. I was shocked to see negligible differences in the contrast of the negatives or the prints from them. Can anyone tell me if it is the developer that is the reason, or have all the years of being taught that agitation will greatly affect contrast, been overstated? The development time for both films were identical.
Denise libby

I wouldn't expect to see significant differences with a 2 bath developer. The first bath has the developing agent, but has a rather neutral pH, so development is at most very slow. The second bath has the alkali, so it creates the needed environment for development, which goes to "completion", meaning that the absorbed developing agent(s) are exhausted. So, yes, agitation is a critical variable during development, but for single bath developers.

hi Denise,

this is a tough situation because from your description the shadows fell out wheras everything else that was sidelit was exposed properly. the best strategy would have been to use a speed gaining developer and reduced development by about 20%. from experience thornton's two bath and foma 100 doesn't give you box speed. the speed gaining approach would have tried to salvage as much of the shadow detail as possible and then using something like slimt printing to increase shadow contrast without affect your highlights which were well exposed. pyrocat at 1:1:200 agitations every five minutes for 45min-60min would have put a bit of a hump in the shadows and left your highlights printable. if you are mixing thornton' two bath, you could also try beutler's which uses the same chemistry. shoot a test shot in daylight with shadows and test. beutler's will give shadow increase and printable highlights - minimize agitations to every other minute and increase time by 30 - 50%. i have found that thornton's two bath does not give you the same control that highly diluted developers and minimal agitation do. with thornton's, the curve is pretty much set by the amount of developing agent (metol) in bath A. with foma 100 and thornton's you would have best let it fully develop the neg with normal agitation. hope this helps.

ps, A bath has 80gr sodium sulfite per litre which is enough to develop the film ;P you'd have to drop it to about 20gr and/or start adding sodium metabisulfite to neutralize the pH.

el wacho said:

ps, A bath has 80gr sodium sulfite per litre which is enough to develop the film ;P you'd have to drop it to about 20gr and/or start adding sodium metabisulfite to neutralize the pH.

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Well, yes, now that I've seen the formula, part A is close to D23, sligthly dilute though, so slightly softer. Some development will occur, but not enough. The contrast gained in the 1st bath wouldn't be that much, so the differences between agitation methods would be negligible anyway.

Agitation has but one purpose, to bring fresh developer to the whole surface of the developing film. Cutting back brings fresh developer to some areas and none or not enough to others thus causing more contrast in the fully replenished areas, less in others. So called surge marks are under agitation caused.

Continuous agitation as in machine processing or agitation every 15 sec in a hand tank will give somewhat more contrast due to continuous replenishement and not letting the developer "use up" in the highlights during rest periods.
About 10/15 % time difference will equal the two methods out.

Time is the proper way to contol contrast, not holding back agitation which only causes problems as I described above. It is the second half of the basic principle, exposure controls the shadows, development controls the highlights. Been that way forever and always will be.

Two bath controls contrast by local exhaustion in the highlights. It used to work well with olde thicj emulsionr film, no longer does. But it always gave lower local contrast in the highlight areas. Agitation has little to do with it so long as you do not over agitate and wash out the A bath in the B bath..

http://www.largeformatphotography.info/twobath/

In some two bath developers contrast is controlled by time in the first bath.

Thank you all for your help. I do know about the agitation/developer exhaustion principle and have used it many times in the past and also water bath development and various ways to compress exposure values by slight over exposure and minus or pull development and all the other tools such as time, dilution, temperature etc., however this is the first time I tested the agitation variable with a two bath developer and was expecting to see a noticeable difference and it simply didn't exist. Alan I have read the thread you cited on largeformatphotography web site which refers mostly to the Stoeckler two bath and again re reading Ansel's The Negative and his use of a variation of the D23 two bath modification but there seems very little written regarding variable agitation or the effects of it on contrast regarding two bath developers, other than the minimum required. I have been a proponent of SLIMT for years and am always amazed by the resistance of so many, to its use and have been dismayed by the vilification of David Kachel by some on this very forum. I did use it in printing the negatives I reference in this thread and delivered the work yesterday and received two large family group portrait commissions from the same clients so it seems the work was more than satisfactory to them. el wacho, I have never used Pyrocat but have used Pyro-Tri for years and have always found it reliable even in extreme dilutions the same with Beutler's in normal dilutions but in this case not with this film and because these were such important photos I just went with a developer I had used successfully in like situations. Thanks again for your help.
Denise Libby