Shelf life of mixed fixer?

Sirius Glass · Dec 15, 2021

Fixers aka hypo generally does not have the oxidation problems that developers have. Hence the posts that the fixer last a long time as long as it has not been expended by use.

MattKing · Dec 15, 2021

I have had fixer sulfur out over time.
I generally mix up 1.9 litres (1/2 US gallon) of working strength fixer at a time, and use it until the earlier of about 75% of the manufacturer's rated capacity is reached or a clip test with T-Max film indicate that clearing times are too long. The bottle I use seals well, and is filled to the near brim.
Usually I reach capacity before their are issues with lost activity but sometimes my throughput is reduced and the time stretches out long past Kodak's one month recommendation for trays. I become concerned when I reach the six month mark.

Pat Erson · Dec 16, 2021

MattKing said:
sometimes my throughput is reduced and the time stretches out long past Kodak's one month recommendation for trays.

For trays Ilford's recommendation is 7 days.

Don_ih · Dec 16, 2021

Sirius Glass said:
Fixers aka hypo generally does not have the oxidation problems that developers have. Hence the posts that the fixer last a long time as long as it has not been expended by use.

There's so much sulphur in rapid fixer, made from sodium thiosulphate and ammonium sulfate and sodium sulfite, I think the sulphur easily starts to drop out of solution (especially if cooled). Regular fixer (slow fixer) doesn't seem to have that problem and lasts a very long time.

Donald Qualls · Dec 16, 2021

Don Heisz said:
There's so much sulphur in rapid fixer, made from sodium thiosulphate and ammonium sulfate and sodium sulfite, I think the sulphur easily starts to drop out of solution (especially if cooled). Regular fixer (slow fixer) doesn't seem to have that problem and lasts a very long time.

All of the sulfur in fixer as produced/sold is in the form of soluble ions (thiosulfate and sulfite, with appropriate number of + signs for each). You only get elemental sulfur due to breakdown of those ions in solution, and reduction of the oxidized sulfur. Which is to say, it doesn't just "fall out" of solution. More likely rapid fixer is more prone to this breakdown because ammonium ion is itself a reducing agent, and is not generally present in old school hypo fixer.

grain elevator · Dec 16, 2021

Pat Erson said:
"Unreplenished ILFORD RAPID FIXER working strength solutions should last for up to :
6 months in full tightly capped bottles"

One word of caution though... I just experienced 1st hand that mixed fixer doesn't keep that long.

I had a 5l jug of Tetenal stuff that I made on Oct.31. 1+4 dilution nothing special.
I fixed 68 films in it over time and yesterday I wanted to use it to fix 34 more films. Well it was dead or semi-dead. I had to make some new fixer and refix the film.
6 weeks and the stuff was toast.

Cavaet Emptor...

Generally it's better to mix a smaller amount at a time. The concentrate is supposed to last longer (although like another poster here, I've had concentrate sulfur out in the unopened, in-date bottle).

Don_ih · Dec 16, 2021

Donald Qualls said:
All of the sulfur in fixer as produced/sold is in the form of soluble ions (thiosulfate and sulfite, with appropriate number of + signs for each). You only get elemental sulfur due to breakdown of those ions in solution, and reduction of the oxidized sulfur. Which is to say, it doesn't just "fall out" of solution. More likely rapid fixer is more prone to this breakdown because ammonium ion is itself a reducing agent, and is not generally present in old school hypo fixer.

That's what I said: rapid fixer is prone to having the sulphur drop out of solution

Shelf life of mixed fixer?

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