Clearing time test for color fixer

[Lemur]

Can the clearing time test be used with color fixer? I use Kodak Flexicolor fixer.

If so, how is the calculation?

In b&w fixer, you have to double the clearing time. For example, if the film clears in 30 seconds, you have to fix for 1 minute… though the recommended minimum time for my fixer is 2 minutes (I don’t get this quite well)

My mix of Flexicolor fixer also clears film very fast, in 30 or 40 seconds. But the recommended time is 6:30. So… how is the calculation? If it is clearing film fast like in the beginning, does it mean that the fixer is working properly?

 

[koraks]

My fuji color fixer clears a strip of b&w film at about the same speed. I use a 3 minute fixing time for color film. Some color chemistry is made for rapid access processing and requires shorter times than the 6m30 listed. I looked up the appropriate fixing time in the datasheet of the chemistry I use and found it was much shorter than the times I found in other places.

If your fixer fixes b&w film within about a minute at room temperature, then I'd say it's safe to assume it will completely fix color film at 38C in three minutes.

 

[BMbikerider]

I don't use any tests, but replenish the fixer AND bleach after each film at the rate of 25cc per film. I also extend the normal times suggested by the chemical makers from 6 mins to 7.

The initial bleach and fix bath is made up to 500cc and after each film, the level is checked and the quantity is reduced to 475cc then the 25cc is made up from the new chemical. The last time I made a fresh new mix is well over a year and I am yet to have a failure. Every so often I filter it via a paper filter usually used for a coffee machine to remove any solids. This way every 20th film means the mixes are completely replaced.

The Chemical is made by Tetenal and as per their advice, I also always use a stop bath which extends the life of the bleach.

 

[Rudeofus]

While color negative film (C-41) starts out as Silver Bromide/Iodide based emulsion just like B&W film, it also contains DIR couplers to reduce contrast. These DIR couplers react with oxidized color developer to form very powerful restrainers, e.g. 1-Phenyl-5-mercaptotetrazole. These powerful restrainers form very insoluble silver salts, which can take much longer to dissolve than what a typical clearing test would suggest.

Your film may look transparent after a few dozen seconds, but these very insoluble silver salts are still in there and can cause trouble down the road. Color negative film is a low contrast medium, which means that the processes following to make a decent image are high in contrast, which means that even small aberrations in a color negative can cause visible defects in the final image.

Note, that not all C-41 fixers are created equal, and that there are different fixer times recommended for different products. Some products are just Ammonium Thiosulfate plus some buffer compounds to get pH reliably up to 6.5, whereas other products are powerful and very fast fixers, loaded with Ammonium Thiocyanate and other compounds to speed up fixation. The 6:30 number may apply to the more simple formulations, but even for fast fixers (clearing time < 20 seconds) recommended fixer times are a few minutes. Make sure you follow the instructions for the exact product you have, and if you are unsure, it's safe to err on the higher side of fixer time.

 

[Photo Engineer]

What he said!

PE

 

[Lemur]

Thank you for all the replies. I really appreciate the information.

I asked this because the fixer I have is “expired” according to Kodak and also the solution I mixed two years ago is way beyond its recommended storage life. Of course, I could prepare and new solution with the “expired” fixer. Or buy new fixer if it is necessary.

So… I guess the clearing time test is not possible for color. Or else maybe it would be well-known.

I also supposed that the fact that the fixer clears film quickly, 30 or 40 seconds, is a good indicator, but maybe that is not enough.

I am giving more details about my experience with this expired fixer in this thread:

https://www.photrio.com/forum/threa...-chemicals-are-still-working-properly.165112/

 

[Rudeofus]

So… I guess the clearing time test is not possible for color. Or else maybe it would be well-known.

In B&W processing, the clearing test tells you two things:

1. How long do you have to fix to get archival stability? (typically twice the observed clearing time)
   
2. Is your fixer exhausted? (typically if clearing time doubles)

In color processing you still get a good answer for question 2, so a clearing test is still somewhat useful.

Note, that fixer at pH 6.5 lasts a very long time, so I would not be surprised of 2-3 year old color fixer still works ok. Also remember that Kodak had to state very conservative expiration dates to cover many different climates and storage conditions, so two years past expiration may not mean much.

 

[Photo Engineer]

An unused color fixer is generally still good if there is no precipitate in the container and if it has no odor other than that of weak ammonia.

PE