I use 10 min for all films and 2 min for paper. Paper fix I toss and the end of each session.
For film I mix up 1.5 litres of working strength, (because that's my largest tank). I figure a recommended 25-30 films per litre and a half and do only twenty, (or throw it after the first batch that takes me over 20.) I tested clearing times after 20 films and it was 3 minutes. Based on the Anchell / Troop recommendation of 3X clearing I do them all at a 10 minute standard time. The reason I'm not so bothered about over-fixing is Troop / Anchell again who suggested that ammonium thio doesn't begin to bleach like sodium thio. Seems to work for me. I would probably test for each batch if I used sodium thio as over-fixing is as bad as under-fixing by all accounts.
The reason I'm not so bothered about over-fixing is
Troop / Anchell again who suggested that ammonium
thio doesn't begin to bleach like sodium thio. Bob H
I haven't the Darkroom Cook Book so do not know just what
was written with regard to sodium thio and bleaching of the
image. With 150 years of it's use the darkroom community
should have well in mind it's short comings and how well
it compares with A. Thio.
Comments this NG usually refer to a very protracted fix
being a cause for bleaching. Most commentary refers to
A. Thio. Most use A. Thio.
A. or S. Thio., the essential ingredient is thiosulfate
which is by itself, if anything, a reducing agent.
S. Thio. as a dry concentrate with Very long shelf life
works well with my current low volume of darkroom
work. I mix it fresh each session, film or paper.
Good for a session with no additives. Also
odorless. I believe Anchell's 'plain' fix
is no more than S. Thio. Dan
You're absolutely right Dan. One shot, right time - sodium or ammonium doesn't matter,they both do a good job.
I go through stages where I may process between 5 and 20 or more films a day so I just wanted to standardize my time without having to run clip tests for each tank load. This way I know that all my films are properly fixed and I felt more comfortable with amm. thio. Also means one fixer, one dilution for my film and paper. The fewer variables I have the less prone I am to screw up. And, trust me - I'm well prone to screwing up.
Acid fixes are more prone to bleach highlights in images than neutral or alkaline fixes. It is a very slow reaction requiring a half hour or more to see any reaction, so I would not worry too much about it.