film clearing time in fixer

As is my custom when trying a new film, I fix a sheet of each new film I'm testing to see how long it takes to clear the undeveloped, fully exposed film in my standard fix which is based on hypo thiosulfate. The two Arista EDU Ultra films, 100asa and 200asa, cleared completely in 2.5 min. but the Efke 50asa took a full five minutes to clear completely. Can anyone tell me why the slower film took so much longer to clear? I'm assuming that the older emulsion form of the Efke has something to do with it but why?
Thanks for the help,
Denise

I really suspect you've some defective Efke film.
There is no GOOD reason why a slower film
should take 100% more time to fix than
some medium speed films. Dan

I assume you were using a fresh batch of fixer?

Most likely a fixer problem, I've used EFKE films for over 30 years and the fix normally.

But then 5 minutes isn't that long for a non rapid Sodium Thiosulphate (hypo) fixer.

Ian

Normally it is usually 2-4 minutes to fix, dependly on how good the fix is. 5 minutes is a on a long side but not uusally so.

Jeff

Jeff Kubach said:

Normally it is usually 2-4 minutes to fix, dependly on how good the fix is. 5 minutes is a on a long side but not uusally so.
Jeff

Click to expand...

Iford's recommended fixing time for films in a simple Metabisulphite/Sodium Thiosulphate fixer IF-2 was 10 to 20 minutes, so a clearing time of 5 minutes is well within expectations.

Ian

Thanks Ian, I didn't realized that.

Jeff

Wirelessly posted (BlackBerry9000/4.6.0.167 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.0.0.0)

Efke 25 is three minutes for me in fresh stew.