Longevity of fixer, again...

Only a few days ago, somebody posted a thread on the longevity of fixer , and he specified that according to manufacturer direction a liter of fixer would be enough for 2 1/2 sheets of 8 x 10 .
I freaked out .... I change my 1/2 liter of solution for 4 x 5 after fixing 20 sheets, and discard 1 liter of diluted fixer only after having processed 10 sheets of 8 x 10 .
I have never worried because the clearing time is extremely acceptable after which i leave the film in the bath for 2 1/2 times the clearing stage .
I have been developing for twenty years now and i have not experienced any problem of sort with my negatives . It seems a little too on the "manufacturer side " to waste so much fixer .
Any input ?
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I 'm not sure if you are thinking about the question I posted or another one similar to it. I said that some manufacturers normally say 1 liter of fixer is enough for 15 - 20 36 exp rolls of 35mm and asked how many sheets of 8x10 that would be equal to.

The answers I got stated that 1 36 exp roll of 35mm is roughly equal to 1 8x10 sheet of film OR 4 4x5 films in surface area.

And I think that for simple self serving reasons the film and chemical manufacturers would love to convince you that you need to buy the equivelant of four liters of fixer every week of the year.

Next time you are in the darkroom put at least twice amount of film through the fixer than they recommend, put the used fixer into a developing tray and slip an unexposed sheet of 4x5 into the used fixer and see how quickly it clears. That is the only real way of determining how much mileage you can get out of it. Keep iterating on this process until you see it degrading in its clearing capabilities. IMHO it is as critical as determining your film speed or development time because it not only optimizes the chemical, but it saves you money that you can use to buy more film. Cheers!

Hi Domenico,

It depends on the dilution of the fixer. For example, Ilford recommends a dilution of 1 part stock Rapid Fixer concentrate, plus 4 parts water. This would be 200ml. stock fixer in one liter of fixer solution. Two and a half sheets of 8X10 film is equal in surface area to ten sheets of 4X5 film, so this is a sufficient amount of fixer to use without exceeding the capacity.

However, Ilford also states that their Rapid Fixer can be used at a dilution of 1 part fixer, plus 9 parts water. This is 100ml. of stock concentrate, plus 900ml. water to make a liter of working solution. Ten sheets of 4X5 film, especially Delta or T-Max, would probably come close to exceeding the capacity of the fixing solution at the 1+9 dilution.

Makw a 5% solution of potassium iodide. After you have used the fixer for one batch of film or paper, add one drop of the Pot Iodide to the fixer (room lights on). If the drop forms a white precipitate that is persistent, the fixer is exhausted. If the precipitate disappears when you swirl it with your print tongs, it's still good to go. There should be no precipitate in fresh fixer. Also, the above post about watching to see how long it takes to clear film is correct. THe fastest and most long-lived fixer I have used is TF-4. Almost instant on 8x10 film....

Fixer is cheap- and your photographs are valuable. Be conservative, test your fixer, use fresh often. 80+ years ago, Alfred Steiglitz used fixer long past Kodak's recommendations- because the film still cleared, and he was certain that the recommendations were a conspiracy to sell more fixer. Now, of course, many of his famous and expensive vintage prints have faded/are fading, and there's not a whole lot that can be done to save them. This per my teacher David Vestal, in his book "The Art of Black-and-White Enlarging".