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 ...
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.
Originally Posted by Photo Engineer
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?
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.