Darkroom 101 - Fixer Question

barbara ann · Nov 19, 2007

Can someone settle a disagreement re: fixers?
I say if you put a couple of drops of Hypo Check into the fixer solution and it turns milky the fixer is exhausted and need to be replaced. My friend says not so. An actual precipitate has to form before the fixer is unusuable.
Which one of us is correct?:confused:

glbeas · Nov 19, 2007

You are right, but with rapid fix you get a milky look that clears when shaken. If it stays milky it's bad. Instructions also say to scoop some up in a small container like a 35mm film can to test with. I always toss mine before it show up as bad so I haven't seen that in years.

Dan Henderson · Nov 19, 2007

I always assumed that that when the hypo check turned milky that WAS the precipitate. I toss when I see the milky color

dancqu · Nov 21, 2007

FirePhoto said:
I always assumed that that when the hypo check
turned milky that WAS the precipitate.
I toss when I see the milky color.

Yes that is the precipitate. A few exact methods
are given for conducting the FT-1 test. I think most
accurate are methods employing some specific amount
of fixer and a certain strength and quantity of test
solution. I've never read of the levels of silver in
the used fixer. Films and RC papers can be well
fixed in fixers very laden with silver. Not so
with FB papers.

I can't use the test myself as I've adopted the use
of very dilute one-shot fix. The silver levels are so
low as to be nearly invisible. Dan

GeorgesGiralt · Nov 21, 2007

Hi !
The main problem with this kind of tests is that it is not quantitative.
If you plan to get the most of your fixer, buy Tetenal fixert test stickers instead. The small tab change color according to the percentage of silver in the fixer solution. A table gives you the quite exact amount of silver into the fixer. This way you'll know if you are overusing it or not.

Akki14 · Nov 21, 2007

Doesn't help with paper fix but for film i always put a cut-off bit of film into the fix and time it. as long as it clears in about 30-35 seconds (in rapid fix) it's fine. When it suddenly decides to take 55s-1m to clear, it's off and i dump it.

Rich Ullsmith · Nov 21, 2007

What Danqu said: for resin papers and film, the fixer just needs to be active, which is easily tested with a scrap of film. Fiber papers act as a sponge, and a two-bath fix is indicated: the first bath to dissolve undeveloped silver, and the second to bring it out of the fibers and into solution. Of course, when the first bath gets tired (measured as Akki says), then dump the first bath, and use #2 as bath #1, and mix a new bath #2.

barbara ann · Nov 21, 2007

I've never heard of Tetenal fixer test stickers. Don't know if they're sold here in the US but they sound like they're just what I need. Perhaps I should have made it clear that I am developing RC paper and not film.

Photo Engineer · Nov 21, 2007

First off, never put the fixer test solution into your fixer. It will decrease the power of the fixer! You must remove a small fixed quantity of your used fixer into a glass container and then drop in a few drops of the test solution.

You will see a YELLOW heavy cloudy precipitate form if the fixer is exhausted. A white precipitate does not indicate exhaustion.

The fixer test solution is Potassium Iodide, and this forms as strong a bond with silver as hypo does. If there is too much silver, then the iodide wins, and you get a precipitate and if there is the right amount of hypo left, the fixer is more powerful and you get a white cloud or nothing at all.

Why yellow? Because silver iodide is bright yellow, thats why. So if you don't see it turn yellow, it isn't forming!

And remember this... The test solution goes bad and so must be discarded if it begins to smell like iodine or turn brown.

PE

dancqu · Nov 22, 2007

GeorgesGiralt said:
Hi !
The main problem with this kind of tests is that it is
not quantitative.

True. And the methods of testing vary. But an useful
semi-quantitative test may be made of it by using the
film strip test in conjunction with the FT-1 test. Simply
clear a film strip then use some small amount of the fix
and test with a drop or two of the standard potassium
iodide solution.

If the strip test shows spent fix but the FT-1 does not
reduce the amount of fix used for the drop test until a
precipitate does form. Very little of the iodide is used
in making a test solution of many many drops. May
be more convenient than strip testing. Dan

removed account4 · Nov 22, 2007

with the "clip test"
you take a small bit of your favorite film
that is exposed by room light
and see how long it takes to clear.
( do this before using the mixed fix for the first time )
when it takes 2x the original time to clear, change your fixer it is spent.

works every time ...

Dan Henderson · Nov 22, 2007

Photo Engineer said:
First off, never put the fixer test solution into your fixer. It will decrease the power of the fixer! You must remove a small fixed quantity of your used fixer into a glass container and then drop in a few drops of the test solution.

You will see a YELLOW heavy cloudy precipitate form if the fixer is exhausted. A white precipitate does not indicate exhaustion.

PE

PE: thank you for the advice on not putting test into the fix. Either my little bottle does not say that or I didn't read the fine print.

Second, I'm assuming a white precipitate precedes the yellow precipitate by some number of prints? If so, am I correct in assuming that dumping the fixer when the white precipitate appears gives a safety margin vs. waiting until the yellow appears?

Photo Engineer · Nov 22, 2007

There will be an early amount of precipitate just because any silver is present, but stirring will cause it to vanish as the hypo dissolves it. The yellow precipitate will form and stay there. It usually settles to the bottom of the beaker as well, but the white stuff generally looks like a wisp of smoke in air.

Iodide in fix slows it down, so continuing to test will gradually weaken the fix if the test solution is dropped into the tray. Also, the test can be rendered inaccurate due to the volume of fix in the tray (or tank).

Using a fixed amount generally damps out the fluctuations in this test and renders it more accurate.

PE

Darkroom 101 - Fixer Question

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