How many rolls can a liter of fixer handle?

The figures are from Ilford's Rapid Fixer technical information (July 2010). The 2 to 5 minutes are the average minimum times for fresh fixer, and the range covers different film types. Ilford agitates 4 inversions in the first 10 seconds and again in the first 10 seconds of each following minute. The sheet also lists 1+9 for paper, but gives a film capacity only for 1+4.

A 5 liter bottle of concentrate makes enough working solution for 600 rolls of 135-36. Ilford adds fresh working solution at 45 mL per roll to keep a bath going, and calls a properly replenished bath long-lived, with 12 months in the tank as a general guide.

Keeping times: unopened concentrate lasts two years at 5–20 °C, and once opened should be used within six months. Unreplenished working solution lasts up to 6 months in a full, tightly capped bottle, 2 months in a tank with a floating lid, 1 month in a half-full capped bottle and 7 days in an open dish.

These come from Foma's one-page fixer sheet (FOMA 04/23). The times above are for the Fomapan 100, 200 and 400 and Retropan 320 rows. Foma Ortho 400 is 3.5 minutes in Fomafix and 11 in Fomafix P. For Fomafix P you dissolve the larger bag and then the smaller in 600 mL of water at 40 °C and fill up to 750 mL for films, and the sheet rates that mix at 15 rolls.

Foma prints no keeping time and no clearing test on this sheet, so there is nothing to quote for either. For automatic processing it uses 1+4 instead of 1+5, which I left out here.

Kodak's beginner guide How to Process and Print Black-and-White Film (AJ-3, February 2016) calls its times approximate and sends you to the instructions in the box for capacities, so it prints none. Liquid concentrates fix in 2 to 4 minutes, powder fixers in 5 to 10, with continuous agitation for the first 30 seconds and then every 30 seconds. With T-Max films Kodak says the fixer is exhausted more rapidly than with other films. A pink stain after fixing may mean the fixer is near exhaustion or the time was too short.

If you use Kodak, take the capacity from the bottle or the pack insert, enter it under "Other" above, and use the clearing-time test below.

A liter of Ilford at 1+4 holds 200 mL of concentrate, which over 24 rolls is about 8.3 mL per roll. A liter of Fomafix at 1+5 holds about 167 mL, which over 17 rolls is about 9.8 mL per roll. That is my division of the makers' numbers, so the two are comparable but not a rating either maker gives. The dilution calculator mixes any ratio.

In a 500 mL tank Ilford is rated for 12 rolls and Fomafix for 8. Capacity scales with the volume of working solution, and the counter above does that sum for your volume.

A roll count is a guide. Ilford's sheet describes a test that needs no counting. Put a drop of the working fixer on a piece of scrap unprocessed film and wait until the spot is clear, which should take around 30 to 60 seconds. Then put the piece into the fixer bath and time how long the rest of the film takes to clear. That is the clearing time, and the fixing time is double it.

Do this once with fresh fixer and write the time on the bottle. Ilford says to discard the fixer when the clearing time in used fixer exceeds twice the clearing time in fresh fixer. Enter both times in the form above. If fresh fixer clears in 60 seconds, you fix for 2 minutes at first and throw the bottle out once the test takes more than 2 minutes.

Ilford also describes two-bath fixing: fix for half the time in the first bath and the rest in a second, and when the first bath reaches its capacity, discard it and make the second bath the first. The film always ends in the fresher bath.