Fixer clip test
Drop a scrap of undeveloped film in the fixer and time until it turns clear. Fixing time is twice the clearing time; when clearing takes too long, the fixer is spent.
Rule: fix for 2× the clearing time. Replace the fixer once clearing takes more than twice as long as it did fresh.
About this tool
Exhausted fixer leaves negatives that fade over time, so it pays to check. Drop a film leader clip into your fixer and time how long it takes to clear, then enter that along with the clearing time of fresh fixer. The calculator returns a recommended fixing time of twice the clearing time, and flags whether the fixer is exhausted.
How to use it
- Time how many seconds an undeveloped film clip takes to clear in your fixer.
- Enter that time along with the known clearing time of the same fixer when fresh.
- Read the recommended fixing time, twice clearing, and the exhaustion warning.
FAQ
Why fix for twice the clearing time?
Clearing shows the visible emulsion has cleared, but full fixing needs longer to make unexposed silver soluble and washable. Doubling the clearing time gives a safety margin so negatives are archivally stable, not just clear.
When is the fixer considered exhausted?
As fixer ages, clearing time lengthens. A common rule is to discard it once clearing takes more than twice as long as with fresh fixer. The calculator compares your two times and warns you when you cross that threshold.