Bleach fix capasity
My current chemicals don't specify blix capasity in the instructions. Usually it lasts much longer than same volume of developer.
Is there an easy way to test bleach fix myself how long I can use it?
Here is a rough test.
Fog some B&W paper and process it normally. It should be totally black.
Blix it in fresh blix and time it as the silver vanishes. Record the time when the silver is gone. Then wash it and observe the color of the paper. It should be cream white after you wash it.
If you do this periodically with blix, when it fails to blix in a reasonable time, then it is exhausted. As long as it will blix the B&W paper, then it is ok at about the same time for color paper.
The same will work for bleach and fix for color film, but you have to use B&W film, and there is a 'correcton factor' for the low silver and lack of DIR inhibitors. This is too complex to go into here so I'll stop.
This is potentially very useful info. It's why APUG is such a good site. Anything which cuts costs is welcome. However what constitutes "failing to blix in a reasonable time"? My blix says 45 seconds, obviously in fresh condition.
Originally Posted by Photo Engineer
I'd accept up to a couple of minutes as there are other things I could do in the waiting time while the print revolves around merrily in the Jobo tank. In fact I have often not done other things rather than risk "overblixing" but I may be worrying unnecessarily. If I have understood you correctly then it may be the sky's the limit in that blix time will increase as it exhausts but provided I am willing to accept this increase then I can continue to use the blix until either it fails to leave the paper creamy white or I run out of patience and replacing the blix is preferable to the extended wait.
Or is there a max blix time beyond which the blix can be considered unsafe. I wouldn't want to risk what appears to be a fully blixed print deteriorating after say 6 months in an album or frame.
If the blix removes the silver and subsequent silver salts from the paper, the paper will be creamy white. The blix is therefore useful regardless of the time and temperature required for silver removal as it goes to completion.
If you wish a more precise test, then use the sulfide test on the washed strip of B&W paper. It should show no residual silver halide, and the retained hypo test should show no test for hypo in the paper after the wash.
If the blix is cloudy and / or smells of sulfur, it is bad. Don't bother to test it, throw it out.
You can try the exhausted fixer test on the blix as well by adding KI solution to the blix and seeing if there is a yellow precipitate. If not, then the fixer portion is still probably working, but if the fixer portion fails, the blix activity goes way way down.
Actually however, everything works in concert in the paper blix. So if one thing fails, all of them fail and the B&W paper in the test I suggest stays brown or black or grey, depending. It is a remarkably easy and accurate measure of blix activity and rate. Just ratio out the proportionate rate of blixing between B&W paper and color paper to make sure that things are being done right with the color paper, as each B&W paper and color paper have different silver levels. You gain experience with practice.
Recalibrate your eyeball every time you change paper types, either the B&W test paper or the color paper brand.