Help with times for Thornton's Two Bath

So, I've decided to try out Thornton's Two Bath. I'm coming from D-76, and am tired of dealing with it going bad on me before I can finish it up. The two bath sounds promising as I shoot roll film quite a bit in very high contrast situations.

So, I will be shooting Acros 100 and HP5+. I'm having a heck of a time finding actual times and speed ratings for these films in Thornton's. I mixed based on the recipe in Edge of Darkness, processing at room temp which will be around 65-75F in my darkroom.

Can anyone tell me what they are using for ISO and dev times? I don't know why I'm having so much trouble - it seems like everyone considers this dev so easy to use that we don't actually need to talk about real numbers!

I would like to work on figuring my own ISO eventually as well, but not really sure where to begin there.

I developed an old roll of Acros I found lying around the darkroom last night, using 4 minutes in each bath and 2 agitations every minute. Negs seem OK to me - the shadows might be a bit thin, but I'm not sure what they should look like in 2 bath, and I don't have them on the light table yet either. That roll was exposed at 100 ISO.

I recon Thorntons two bath loses about 2/3 stop in shadow speed compared to D-76 with Delta 100 and 100 T-max although acutance and grain are very good.
There are other two bath developers that actually give a speed increase like Emofin and Diafine.

Thornton said 4 minutes in each bath for roll film, and 5 minutes in each for sheet film, at 21 degrees C. See www.barrythornton.com

The formula on that site is slightly different than the formula in the book. I had an Email exchange with Thornton before he passed away, and he confirmed that the formula in the book was the most recent and preferred formula.

For all films, regardless of speed? I guess it is easier than I thought ...

Jeff Bannow said:

For all films, regardless of speed? I guess it is easier than I thought ...

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Yes. You can mix different films in the same tank or tray.

I've been using the table at the end of the article at http://www.largeformatphotography.info/twobath/ and it has really helped control contrast in some tricky situations. I haven't timed it to the second, but I remain in the neighborhood and it works well. That formula (Stoeckler) differs from Thornton's, IIRC, in insignificant ways as far as chemistry goes. Even if I'm wrong about that, it still works with both.

The stuff works forever, it seems (12 5x7's in one 1-liter batch and still developing), and you can tell when it starts to weaken.

I have read, however, that development times differ for different speed films in this stuff, and I myself have had some huge disappointments based on that aspect. The times on the above referenced site apply to ISO 400, as the article says.

Bath A is slightly alkaline and behaves like D-23 so some development will occur in it. Thereore time and temperature are important. This is true for most two bath developers unless the pH of Bath A has been adgusted so that it is not alkaline. The time in the second bath is unimportant as long as it is sufficient to complete development.

The time in Bath A for a particular film can be calculated if you know the development time in D-23. I don't remember the exact factor but I think it is something like 1/2 to 2/3 of the D-23 time. You should be able to calculate it by looking at the table values vs the D-23 times.

Bath A should last for months even with heavy usage, just top it off with fresh. Bath B should be replaced when it becomes badly discolored.

i'd be interested to know how you could reconfigure the A bath with a combination of sod sulfite and sod metabisulfite to neutralize any development in bath A and just use a B bath of sod carbonate say 20g/L to do all the development. i imagine that would be closer in look to a true two bath look...

Jeff, from experience i shot most films at half box speed to get good shadows with your formulation. yes you can throw most film together - i remember Barry Thornton saying something about some extremes wouldnt work optimally like a 3200 iso film with techpan because the techpan film needs to be pulled out a little earlier from the B bath ( or perhaps for techpan you could use something like a 6g/L borax B bath ).

el wacho said:

i'd be interested to know how you could reconfigure the A bath with a combination of sod sulfite and sod metabisulfite to neutralize any development in bath A and just use a B bath of sod carbonate say 20g/L to do all the development. i imagine that would be closer in look to a true two bath look...
.

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For a neutral pH for Bath A just use D-25. However, some people find that true two bath developers do not work well with modern emulsions and produce thin negatives. Modern emulsions may need some development in Bath A to produce satisfactory results.

I disagree with the above statement based on experience. Diafine works fine with modern emulsions and it is a "true" divided developer. The same is true of the divided Pyrocats, based on experience of others, including its inventor, Sandy King.

I divide the sodium sulfite in Thornton's formula 50/50 between the A and B baths. I don't think this eliminates development in the A bath, but believe it does reduce it.