Running a two-bath fixing rotation

Purpose

To make sure the last bath a negative or print meets is close to fresh, so that nothing leaves the fixer still carrying the invisible sparingly soluble compound that no amount of washing will remove.

When to use it

Anything you intend to keep, and every fibre-base print without exception. A single bath is enough for a work print you will throw away this month.

It does not replace the clearing-time test or the capacity log. Two baths change which bath is worn out first; they do not stop one wearing out, and the rotation only works if somebody is measuring.

Before you start

You should already know why the rotation exists rather than merely how it runs, from fixer capacity and exhaustion, and what an exhausted bath leaves behind, from the exhausted-fixer break/fix page.

On the bench: two vessels of equal volume; enough fixer for both at one dilution; two labels written before either is filled, by the labelling procedure; scrap film for the clearing-time readings; the capacity log, ruled with a column for each bath; and the silver-bearing waste container, open and labelled.

Procedure

1. Mix both baths from the same product at the same dilution to the same volume. The second one is the one that matters, so it starts fresh and stays that way for as long as the rotation lasts.
2. Label them bath 1 and bath 2 — in words on the bottle, not by position on the bench.
3. Measure the fresh clearing time in each by the clearing-time test and write it on both labels and in the log.
4. Fix for half the recommended time in bath 1, agitating as your processing procedure specifies. For film the recommended time is twice today’s clearing time; for paper it is the maker’s published figure for that paper.
5. Drain, then give the other half of the time in bath 2, with the same agitation.
6. For a fibre-base print, hold the total time down rather than up. The published optimum-permanence figure is one minute at 1+4 in fresh fixer, and the maker’s instruction is not to extend it: a longer time and an over-loaded bath both make the wash harder, which is the opposite of what a doubtful print needs.
7. Add the session’s area to bath 1’s running total in the log. Bath 2 carries a total too, but it is bath 1 that decides the rotation.
8. Measure bath 1’s clearing time on the schedule the log sets, and always before work you care about.
9. When bath 1 crosses the retirement criterion — today’s clearing time more than twice its fresh figure — stop using it and finish nothing else in it.
10. Discard bath 1 into the silver-bearing container by its own procedure, and take the route the disposal caveat tells you to go and find, not a drain.
11. Promote bath 2 to bath 1. Write a new label; do not amend the old one, and carry its own measured clearing time across as its history rather than as a fresh figure.
12. Mix a fresh bath 2, measure its clearing time, label it and open a new column in the log.

How you know it worked

• Every sheet and every film went through both baths, in order, for half the time in each.
• Bath 2 has never been the first bath a loaded material met.
• Both bottles carry a fresh clearing time, a date and a running total, and the log agrees with them.
• The rotation has a written history: which bath was promoted, when, and at what clearing time.
• On a fibre print, the fixing time was short and in fresh fixer, and nobody extended it because the print looked doubtful.

If a step fails

Step 1, the two vessels are not the same volume. Rotate anyway, but log both volumes and treat the smaller bath as the one that will cross first. Unequal baths make the sheet-count arithmetic useless; the clearing time still works, because it measures the bath rather than counts the work.

Step 4, a sheet is left too long in bath 1. Note it and carry on into bath 2 for its normal half. An over-long first bath costs washing, and the print’s own answer comes from the residual tests rather than from a second opinion.

Step 5, bath 2 was skipped for a batch. Those pieces have had half a fixing time in one bath. Put them back through the full sequence in fresh fixer before they dry — after a soak in water — and write down which batch it was.

Step 9, you find bath 1 already past the criterion. Everything since the last measurement is suspect. Re-fix what has not dried in a fresh bath, and test what has by the residual-silver arm of the residual tests; the yellowing it finds cannot be washed out later, so finding it now is the only cheap moment.

Step 11, the labels were swapped or the promotion was not written down. The rotation has lost its history and neither bottle can be trusted as the fresh one. Retire both, mix two new baths, and start the log again. That is cheaper than one print you cannot explain in ten years.

What to record

Two columns in the capacity log, one per bath: the mixing date, dilution and volume; the fresh clearing time; a line per session with the area through it and the running total; every clearing-time re-measurement with its date; and the promotion events, each with the date, the clearing time at which bath 1 was retired and the label written for its replacement.