Using the Ilford recommended film strength fixer for 30 sec for RC and 60 sec for Fibre based paper saves a lot of time. But, with it sitting in open trays how easily can it be tested to see when it is losing too much strength & needs to be dumped? Normally I use a piece of film, agitate it in the fixer tray & see if it clears within 30 seconds. Longer than that, I dump it & mix new. Is this an accurate way to test?

-- Dan Smith (shooter@brigham.net), October 23, 1997

Answers

No, it's not accurate. Fixer doesn't actually "lose strength", it acquires dissolved salts that make it lose effectiveness. The cabability of it to remove anti-halation backing is not related to its ability to remove unexposed halides.

It's a complicated topic, and I read up on it recently, but unfortunately can't remember where on-lines. Many technical textbooks describe what is going on.

My own technique is: for film fixer, when the clearing time doubles, it's time to change the fixer. For paper, I keep a track of how many sheets have been through, and change it according to the manufacturer's instructions.

There are chemical tests available for testing fixers, but I have no experience of them.

-- Alan Gibson (gibson.al@mail.dec.com), October 24, 1997.

See: http://www.silverprint.co.uk/p37.html

The chemical equation didn't come out in this on-line version of a printed catalogue. These are:

AgBr + (S2O3)2- --> Ag(S2O3)- + Br-

Ag(S2O3)- + (S2O3)2- --> Ag(S2O3)2 3-

Ag(S2O3)2 3- + (S2O3)2- --> Ag(S2O3)3 5-

-- Alan Gibson (gibson.al@mail.dec.com), October 26, 1997.

Dan,

I ran across another, simple fixer test while doing some reading and thought I would pass it along.

Henry Horenstein offers this method as a more accurate means to test fixer exhaustion than the film clearing test.

Mix:

Kodak Rapid Selenium Toner...10 milliliters Water to make...............100 milliliters

1. Use a print that has been processed in the suspected fixer.

2. Place a drop of the diluted solution on a squeegeed, white margin of the print (or a clear part of film).

3. Wait three minutes; then wipe off the drop with a clean blotter or cloth. If the test leaves any discoloration other than a slight cream tint, the fixer is exhausted.

-- Fred Schmidt (driko@ix.netcom.com), October 30, 1997.

Testing fixer

There are two products that will check fixer for dissolved silver halide: Edwal's Hypo-Chek and Nacco's Naccocheck. Scoop out a few ml of fixer from the tray and drip a couple of drop into it. If clouds form, the fixer is bad. Fixer is cheap. When in doubt, throw it out.

-- Michael D Fraser (mdfraser@earthlink.net), November 26, 1997.

A quick and dirty check we used to do in the Navy photo lab was to drop a shiny new penny into the fixer tray. If it plated silver, there was a good deal of silver in the fix and it was probably time to think about changing it. (Dont dump heavy metals -- reclaim them!)

The various chemical testers mentioned above will be a lot more accurate.

-- Tony Brent (ajbrent@mich.com), September 22, 1998.

Get some Edwal Hypo Check. They say the 0.5oz bottle is good for 800 tests and I beleive 'em. It's about $3 from B&H. Also, a two bath fixing routine is more trustworthy.

-- Tim Brown (brownt@ase.com), September 23, 1998.