Tools
Fixer calculator
Dilution, silver loading and capacity, worked against the limits Ilford actually publishes rather than the one number on the front of the sheet.
Dilution
Ilford writes fixer dilutions as 1+n: one part concentrate to n parts water, so 1+4 is one in five and not one in four.
- Concentrate
- 200 ml
- Water
- 800 ml
- One litre of concentrate makes
- 5.0 litres
Paper: silver loading
What a bath has taken, against the four separate limits Ilford publishes for it. The capacity table on the fact sheet is not one of them, and that is the whole difficulty: its headline 40 prints per litre is the same number as the commercial-permanence limit, with no archival headroom underneath it.
- 8×10 equivalents
- 20.0
- Silver in the bath
- 1.00 g
- Concentration
- 1.00 g/l
Against the fibre-based limits
- Maximum stability in long-term storage — limit 0.5 g/l. Exceeded. This bath is at 1.00 g/l.Rapid Fixer and Hypam sheets, ≈ 10 8×10 FB per litre
- Commercial image permanence — limit 2.0 g/l. Within it, at 1.00 g/l.Rapid Fixer and Hypam sheets, ≈ 40 8×10 FB per litre
Throughput is a guide, not a measurement. Ilford is explicit that silver loading depends on the ratio of exposed to unexposed area, so a litre that has taken ten heavy prints is not in the state of one that has taken ten near-white ones. Estimator papers are, in Ilford’s own words, “usually not sensitive enough to test the very low silver levels suitable for optimum permanence” — which is exactly the 0.5 g/l case.
Film: capacity used
Ilford gives 24 rolls of 135-36 per litre at 1+4. No silver-per-roll figure is published, so this reports progress against that capacity rather than converting it into a concentration we would have had to invent.
- Stated capacity
- 24 rolls
- Used
- 50%
This is a fixing-performance figure, sitting inside the 8–10 g/l tolerance band for film baths. It is not an archival criterion, because for film the archival criterion is not bath silver at all — it is residual thiosulfate retained in the material, and no bath test measures it.
Every figure above is read from an Ilford fact sheet — Rapid Fixer and Hypam, August 2002 revision, and 2000RT, March 2002 — and the reasoning behind each is set out in What fixer exhaustion actually means, which cites them. Figures apply to those products; another manufacturer’s fixer is another manufacturer’s problem.