optimizing fixing and washing

[Bruce Watson]

I'm just switching over from Tri-X to 400Tmax in 4x5 sheets. It occurs to me that, while I have film development nailed down (EI and development times) via Zone System testing, I don't have fixing or washing equally well nailed down.

How does one tell how much fixing is enough? I'm not talking about a rule of thumb like "twice the time to clear." I'm asking if there is a test for residual silver halides -- something like the residual hypo tests used to determine wash times. I'm thinking that I could run an unexposed sheet of film through the process and establish a time for it that would be a worst case for properly exposed sheets maybe.

As for washing, is a residual hypo test still the best way to determine when sufficient washing has occurred? If so, who makes the best test kit?

 

[Lowell Huff]

The Methylene Blue Test is to determine residual thiosulfate in the emulsion. Unless you need this for a contract clause, it is a waste of time and money, as is washing for more than ten minutes.

 

[dancqu]

I'm thinking that I could run an unexposed sheet of film
through the process and establish a time for it that would
be a worst case for properly exposed sheets maybe.

As for washing, is a residual hypo test still the best way
to determine when sufficient washing has occurred? If so,
who makes the best test kit?

I've done that but with roll film. Years ago I established
minimum fixer requirements and times. The idea was to
use fixer one-shot without tossing excess fixer down
the drain. I Develop film one-shot so why not Fix
film one-shot.

Twice clearing and the FT-1 tests do not work when
establishing minimums. So I've settled on amounts and
times which yield entirely clear, colorless or very near
so, film; worst case testing, no exposure. Then the
amount is bumped some very little for allowance
and quicker fixing.

As for washing a method akin to the Ilford Sequence
with room temperature water plus a Photo Flo does
it for me.

The HT-2 test is a silver for residual sulfur test. The
Ilford method for the test requires only silver nitrate
at correct dilution. Dan