Two bath developers are compensating developers because they utilise the exhaustion of the developing agent and stop processing the highlights when they are complete. Barry Thornton’s formula is the most up to date and was specifically formulated to give very good results with modern film emulsions.

Thornton’s formula is largely based on a mix of Divided D-23 and Stoekler's 2-bath. However, he didn't want D-23's softness due to the high sulphite level. So Barry experimented and found the magic level of sulphite was 80g per litre. This was where the D-23 softness was considerably reduced. You can process 15 rolls of film through his 2-bath - which is somewhat more than the Stoëckler and Adams D-23 variants.

Barry Thornton’s Higher Definition Two Bath

Bath A
Metol 6.5g*
Sodium Sulphite 80g**
Water to 1 litre

Bath B
Sodium Metaborate 12g
Water to 1 litre

* A later version increased the metol from 6.25g to 6.5
** This same later version lowered the sulphite to 80g


Using a Two Bath developer

All two bath developers are used in a similar way:

• Do not pre-wet the film!
• Pour in Bath A and rap the tank to dislodge any bubbles sticking to the film.
• Agitate gently for the first 30 seconds to one minute to completely soak the emulsion.
• Agitate for 10 seconds each minute.

After bath A, pour off the liquid and save it for future films.

Note: Do not rinse or stop the film between baths.

• Now, pour in bath B. In bath B the development really gets going as the bath is composed of the accelerator. Agitate for just 5 seconds and rap the tank to dislodge air that might stick to the emulsion.

• Agitate for 5 seconds every minute. Then pour bath B out and save it too. Bath B can be re-used also.

• Stop and fix as usual.

Thornton's two bath works very well at around 4.5 mins in A and 4.5 mins in B. Use that as a starting point.

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