Stupid question about testing fixer.

simon ess

simon ess

Just call me Roxanne.
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I think I know the answer to this but I'm feeling a bit thick and just want to make sure.

To test if fixer is still ok I drop in a small piece of unexposed, unprocessed film and time how long for it to clear.

Fix for about double that time.

Have I got that right?
 
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The film needs to be exposed AFAIK, e.g. a piece off the leader from a 35mm roll but otherwise, yes twice the clearing time
 
I usually put a small drop of fixer in the centre of the test piece, and then drop the piece into the fixer a minute or so later. Then I time how long it is until I can't see the dot anymore. I find it hard to tell when a piece of film has gone clear, so comparing the rest of the piece to the clear dot in the middle is a lot easier.
 
sirch said:
The film needs to be exposed AFAIK, e.g. a piece off the leader from a 35mm roll but otherwise, yes twice the clearing time
Click to expand...

Thanks. So if I had a piece of bulk roll film I just expose it to light before testing?
 
Carl Hall said:
I usually put a small drop of fixer in the centre of the test piece, and then drop the piece into the fixer a minute or so later. Then I time how long it is until I can't see the dot anymore. I find it hard to tell when a piece of film has gone clear, so comparing the rest of the piece to the clear dot in the middle is a lot easier.
Click to expand...
Thanks Carl. That makes sense.
 
sirch said:
The film needs to be exposed AFAIK, e.g. a piece off the leader from a 35mm roll but otherwise, yes twice the clearing time
Click to expand...
No, in normal use you are removing the unexposed parts of the emulsion - the exposed parts are already turned to silver metal. It makes no difference whether the film is exposed or not so long as it is not developed. In practise, the test portion will be exposed by the time you get it into the fixer but it doesn't need to be. If you get your chemicals mixed up, you can 'fix' an entire roll of film - exposed and unexposed parts.
 
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It doesn't matter what part of the film you use for this clip test. If you cut off a small piece and drop it into a quantity of fixer in daylight, then it is by definition 'exposed, 'fogged', or what ever adjective you choose to use. If it ever had any latent image on it, then as soon as it was exposed to daylight, it will have been obliterated.
I usually measure the time it takes to clear in a small glass containing fixer and if 3 times that is within my normal fixing time, then I consider the fixer to be OK.
 
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