B. Thornton 2 bath dev - push times?

Hallo,
Can anyone give an indication of % increase in times for push-processing one and two stops with Barry Thornton's 2 Bath Developer?
I was thinking around 25-30% increase per stop - any thoughts welcomed. I have not found a reference to push-process in his formula lists. (*other developers would be better for push-process but looking for % increase with this developer*) Any thoughts welcomed.

Sim2.

Thornton's two-bath developer is a very good developer with excellent compensating effect and a great balance between tonality, speed, fine grain and acutance. It is, however, totally unsuitable for push processing. Thornton published an N+ variant of the Bath B that raised the Sodium Metaborate from 12g to 20g of Sodium Metaborate.

This N+ version of Bath B is useful but not in the sense of a strict +1 stop expansion (which can be much better achieved by selenium toning the negative). If I photograph something that has dark shadows and bright highlights but also a significant part of the scene is relatively lacking in mid-tone separation then I use the N+ version of Bath B. Having said this, I use the N+ variant extremely rarely.

If you want to push your film speed, you will be much better off using a developer designed for that purpose.

Bests,

David
www.dsallen.de

If I was going to push film, I would not start with this developer. *But* if you really want to do it, you have a couple of options.

a) You can increase the bath A time. This is similar to extending development in D23 (not exactly - Thornton's A formula is not as alkaline). The Bath B time won't matter much, so the usual 3-5 minutes should be fine. How much work the second bath will do, and what it will do with the density curve is up to you to find out.

b) Replace the B bath with sodium carbonate for single use. That is more alkaline than the 20g sodium tetraborate option, and will punch up the compensation and the effective speed for some subjects.

You do not say what you plan to photograph. If it is a low contrast scene, the I'd look at option (b). It it is a high contrast scene (stage work, perhaps), look at option (a).

You will have to run tests. This developer is unusual in that development occurs in both baths, and your controls for bath A are time and temperature, and bath B are alkalinity and temperature (with time as a minor variable). This makes for a non-linear response. I presume that you will be developing by inversion - things change a bit using rotary development.

Personally, I'd look at a different developer with some documented push behavior rather than mess around with the Thornton one. And I use the Thornton developer for most of my work at the moment

A good two bath developer for pushing film should contain Phenidone or a phenidone derivative and not Metol. Despite its cost Diafine would be a good choice. You might check on APUG and the web for Diafine substitute formulas.

Lol! Well, I reckoned that it was not the best choice for pushing as I could find no reference about push-process! It is just that I found a roll of film marked to push and don't have any other dev mixed, probably a couple of years old and no idea what's on it, so not a lot to lose really.
At least the explanation that a push dev should have Phenidone rather than Metol based gives a clue as to why BT2BD is not for pushing. Thanks for the input, appreciated.
Sim2.

In absence of a purpose designed developer, Thornton's 2 bath is quite similar to the Stoeckler, which gives a small push as illustrated in Fig 1 here:
http://www.largeformatphotography.info/twobath/

You could try the phenidone based 2 bath formula described here.
(there was a url link here which no longer exists)
I have tried this with Fomapan 100 rated at 400 testing a 4x5 hack and it worked well at 400. I used 5 min at 100 and 6min at 400 in each bath for sheet film, less gave me patchy development and I may still have play around with agitation.

Thanks for all the input - appreciated. May give the phenidone version a try, in time, or just remember to expose correctly in the first place
Anyway, fun to hear all the options!
Sim2.

so an attempt might be to divide FX-37 (hydroquinone/phenidone) ?