Well this is a yardstick that don't measure up to the job!
Originally Posted by Greg Davis
I'll explain that in simple terms.
A 35mm film is about 0,06 m2
Fixer is about 20% solution
In the film remains about 12 ml fixer absorbed in the emulsion, that is about 15 gram of solutiion.
Weight of fixer 15g x 0.20 equal to 3 gram fixer in the film.
Filling the tank from emty dilutes everything 1:20 and after a very short time equilibrium between concentration in film and water is reached (this time gets slightly longer as the concentration sinks)
Concentration before washing 3gram / 0.06 m2 = 50 gram per m2
1. tank 50 g/m2 : 20 = 2.5 g/m2
2. tank 2,5 g/m2 : 20 = 0.125 g/m2
3. tank 0.125 g/m2 : 20 = 0.00625 g/m2
4. tank 0.00625 g/m2 :20 = 0.0003125 g/m2
5. tank 0.0003125 g/m2 :20 = 0.000015625 g/m2
6. tank 0.000015625 g/m2 :20 = 0.000000781 g/m2
7. tank 0.000000781 g/m2 :20 = 0.000000039 g/m2
8. tank 0.000000039 g/m2 :20 = 0.0000000002 g/m2
The "yardstick" is meaningless already, it goes straight from 4 to 1 between tank 2. and tank 3.
And any difference from then on in these measurements is just random variations, and a single drop of fixer residue on one finger during the test will ruin everything as far as the hypotester goes.
You can calculate the same with running water, only difference is that it uses more water, long enough - and it is good enough.
The variation between non-hardening and hardening fixer, is also a matter of time mainly. Hardening fixer will take more time to reach equilibrium. In Ilfords method this is simple : use minutes, as a time measure, instead of seconds.
3 tanks of water is enough, 4 is plenty!
10 changes of water, according to Kodak, is a way over the top.
More time in running water will simply mean you use more water, if that is OK, the end result will be fine.
Hypo test agent is a waste of time, it is in effect a GO - NO GO measure test that can be used just one time, to self-assure that you do things right.
Disclaimer : I'm talking FILM here, paper is a different matter, since the different bases behaves way different as far as absorption of fixer goes.
But having several trays for washing - shifting from one to another, clean one is always better in theory than running water, IMHO.
Last edited by Removed Account2; 11-23-2010 at 08:05 PM. Click to view previous post history.
Reason: Expanded 'til 8. tank