Originally Posted by Photo Engineer
The original post by Greg Davis showed the amount of Thiosulfate residue in film regardless of wash condition. The wash is irrelevant as long as you get to the lowest level (archival quality) or next to lowest (commercial quality). For those that brought up this topic before, there are indeed 2 ANSI standards as noted here.

In any event, you invoke arguments shown later in the thread to be theoretical and as stated from posts #33 onward, the actual data from practical experiments always wins. If a given wash is sufficient to achieve a given condition, then it works. Change the temperature, water supply (hardness and etc) and all bets are off. You have to do the tests all over. And, your calculations would have to include this type of variable as well, which it does not.

Bottom line... I trust Greg. But I would verify with my own work flow and wash water as an initial starting point!

PE
Density of Stain vs. Estimated Grams of Thiosulfate Ion/sq. meter
1=0.01
2=0.02
3=0.05
4=0.12
Well this is a yardstick that don't measure up to the job!

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

Look at these numbers once again:

The test goes down to 0.01 g/m2. If that is archival quality, fine by me.

But the number show that 3 tanks after the Ilford method is already at a theoretical limit of 0.006 g/m2 in my book that is already past what you can HOPE to measure, by your indicated measuring method.

Now, I was under the impression that the Ilford method was not up to archival standards, I was assuming that we need to reach at least 0.001 or lower (from memory). That will be reached by more changes of water, easily and effortlessly.

But you cannot measure THAT by this method, you don't have maesuring RESOLUTION down to that level with this method.

Is that concept so damn hard to grasp?