Quote Originally Posted by Greg Davis View Post
According to the data sheet that came with the Hypo Estimator:
Density of Stain vs. Estimated Grams of Thiosulfate Ion/sq. meter
1=0.01
2=0.02
3=0.05
4=0.12
Now its just as simple to calculate this for running water also, and it will give just as good results - given enough water and time. Proponent for this procedure is that it takes care of itself, once set up, and if one has control over the water temperature, in case variations gives rise to reticulation.


First always take into account that the first tank filling, until overflow is exactly the same as the first tank filling in the Ilford procedure! Therefor one does NOT start from max concentration in the film, but from 1/20th of that. After that its just a case of simple dilution.

Like before there's 50 gram thiosulphate per square meter film to start with.

During slightly less than the first minute concentration is reduced to 1/20

Start : 50 g/m2

1 minute : 50 g/m2 : 20 = 2.5 g/m2

5 minutes dilution : 4,75l water, dilution 1:7.5
concentration after 5 minutes : 2,5 g/m2 :7.5 = 0.333333 g/m2

10 minutes dilution : 8,5l water, dilution 1:9
concentration after 10 minutes : 0.3333333 g/m2 : 9 = 0.0370 g/m2

20 minutes dilution : 17,0l water, dilution 1:17
concentration after 20 minutes : 0.0370 g/m2 : 17 = 0.002178 g/m2

30 minutes dilution : 25,5l water, dilution 1:17
concentration after 30 minutes : 0.002178 g/m2 : 17 = 0.000128 g/m2

40 minutes dilution : 34,0l water, dilution 1:17
concentration after 40 minutes : 0.000128 g/m2 : 17 = 0.0000075 g/m2

I think its pointless to continue this, compared to the Ilford method, which is exponential, this method instead is a steady dilution, it takes longer, it uses a lot more water, but it's less work, once set up.

IMHO there's little point continuing after 30 minutes, the concentration is already archival levels, just as 4 changes of water according to the Ilford method is more than adequate.

If one uses hardening fixer, one needs more time, if thats the case 40 minutes might not be enough. But 6 changes of water, while one let the tank stand long enough to reach equilibrium between water in the tank and fixer remnants inside the film layers certainly are!

You choose your way of work, and can rest assured that both ways will work adequately, one you adjust to the chemicals you use, and makes sure your clean and don't contaminate with fixer left on the bench etc etc etc, remember we end up with virtually clean, nearly drinkable water inside that tank!