Some DIY fixer questions

Hi. I recently started mixing my own chemicals and I have a couple questions about DIY fixer.
One, how do I determine the fixing time for paper? I know about the 2x clearing rule for film, but I've seen some people say that it doesn't work for paper, so what rule should I use for paper?
The fix i'm using clears in at least 30 seconds and maybe faster, from my tests.
Two, the fixer has a distinct ammonia smell, but the fixer is a neutral fixer, and I thought that neutral fixers were supposed to be odorless. Am I wrong about this, and either way, how do I get rid of the smell?
This is the formula i'm using.

Rudeofus or one of the other chemists here will likely give you more detailed information soon, however, what you are using is a rather standard rapid fixer. Fixing times will depend on the dilution, but at "print strength," which is weaker than "film strength," the times should be in the one-minute range for RC papers and around 2 minutes for fiber-base papers. Throughput capacity will likely be similar to other rapid fixers, like the Ilford product here: https://assets.website-files.com/5b...3a2b1b17efb_tech specs ilford rapid fixer.pdf

If you smell ammonia, the pH is likely more alkaline than neutral. Adjusting the pH of your fixer (maybe by adding more metabisulfite) might fix the problem.

Best,

Doremus

This formula is actually used with the same dilution for both film and paper. Would that decrease the times noticeably? (I know with Ilford fix it goes down to 30 seconds for paper at film strength, but I don't know whether that applies with this formula since it uses the same dilution for both.)

Peter T said:

Would that decrease the times noticeably?

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Probably, but at some point you'll hit upon the limits of how rapidly the liquid can permeate the emulsion. In my experience it takes at least 15-20 seconds for a processing bath to soak into an already-wet emulsion at room temperature, so any fixing time that approaches this 'hard limit' will be suspect.
So I'd stick to a 1-minute fixing time as a bare minimum.

Why neutrality? Any reason?

Slight alcaline fixer washes better off any emulsions

You can test print paper for retained silver to determine minimum fixing times. The test solution can be made from selenium toner.

ruilourosa said:

Why neutrality? Any reason?

Slight alcaline fixer washes better off any emulsions

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I want an odorless fixer, and a neutral fixer gives me that. Would what you mean by slight alkaline also be odorless?

bdial said:

You can test print paper for retained silver to determine minimum fixing times. The test solution can be made from selenium toner.

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Sounds good. I'll give that a try.

Also, in terms of adjusting the pH, what's a good amount of metabisulfite to add as a step? I want to make sure it doesn't turn acidic, as that would significantly decrease shelf life.

Peter T said:

Hi. I recently started mixing my own chemicals and I have a couple questions about DIY fixer.
One, how do I determine the fixing time for paper? I know about the 2x clearing rule for film, but I've seen some people say that it doesn't work for paper, so what rule should I use for paper?
The fix i'm using clears in at least 30 seconds and maybe faster, from my tests.
Two, the fixer has a distinct ammonia smell, but the fixer is a neutral fixer, and I thought that neutral fixers were supposed to be odorless. Am I wrong about this, and either way, how do I get rid of the smell?
This is the formula i'm using.

Click to expand...

fix unexposed paper for a certain time then rinse and develop normally in white light to check if that fixing time was adequate.

That's what I'm doing now, it's how I know it clears in 30 seconds at max, but I would think that determines the clearing time, not the actual fixing time. Does paper not need extra time past clearing?

Peter T said:

That's what I'm doing now, it's how I know it clears in 30 seconds at max, but I would think that determines the clearing time, not the actual fixing time. Does paper not need extra time past clearing?

Click to expand...

You should fix for a minimum of twice the clearing time, hence 60 seconds minimum for the particular paper you are testing. You don't say if you are using RC or fiber-base paper. If the latter, then the fixing time seems to jibe with Ilford's "film-strength" fixing regime. One minute might be the practical shortest time even for RC paper, since the fixer takes some time to diffuse into the emulsion and get working.

In any case, I'd test for residual silver. With selenium toner it's easy: Mix KRST 1+9 from concentrate to make your working solution. Place a drop of this on the clear white border/area of a fixed and completely washed print and let it sit for three minutes. Rinse and inspect the area. Any tone other than a very faint cream color indicates inadequate fixing. FWIW, my prints on a variety of papers never even show the slight cream color; the tested area is indistinguishable from the rest of the paper white.

If you fix a few strips for various times in fresh fixer, some too short, some in the middle and some way too long, you'll be able to test them and pinpoint the point where fixation is just barely adequate. Add a generous safety factor to that (2x or more, since you'll be using fixer till it is exhausted) and you'll have a usable fixing time for prints. The, test again for the fixer exhaustion point, i.e., where fixing becomes inadequate after running lots of prints through the fix at your fixing time. Find the number of prints you can fix till you get to that point, add a generous safety margin (e.g., 15% fewer prints than the limit) and you now have both fixing time and throughput capacity. Then just test the last print through a batch of fixer to make sure everything is alright as a control.

Best,

Doremus

I'm using RC paper. The actual clearing time might be lower than 30 seconds, as I didn't test any lower times. So if I can get a 15 second clearing time than I should be able to use a 30 second fixing time right? 1 minute can't be the minimum for RC paper since Ilford fixer at film strength can fix RC paper in 30 seconds.

Ok, good to know. That fully answers my first question. About the second question, dealing with the fixer smell (too high pH), when i'm adding the metabisulfite to make it neutral again, how do I make sure the pH doesn't turn acidic? Do I need to get a pH meter?

In respect to the issue of how short a fixing time can be used, if you are aiming for a short fixing time, ensuring even immersion and appropriately thorough agitation may be the most important concerns.

How does agitation and immersion conflict with pH adjustments to remove smell? I'm very confused.

Peter T said:

How does agitation and immersion conflict with pH adjustments to remove smell? I'm very confused.

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It doesn't.
My post was intended to follow michael_r's post dealing with short fixing times - but you got your intervening post in before mine showed up.

I didn't think it did, the last four posts ended up in a bit of a mess. MattKing's first post was supposed to reply to you Micheal, but I got my post in before he got his in. I'm going to report this post so a moderator can maybe clean this up.

I do think I've got my questions answered now though, so thanks for the help!

I don’t think we have a way of changing the order of posts, unless maybe Sean could mess with the time stamp, but we’ve never done that.

And I clarified my post, in order to make it clear what was being addressed.