[pure-silver] Non-acid rapid fixer - continued

  • From: Claudio Bonavolta <claudio@xxxxxxxxxxxx>
  • To: Pure-Silver <pure-silver@xxxxxxxxxxxxx>
  • Date: Thu, 18 Feb 2010 13:15:37 +0100

Following my quest for a non-acid rapid fixer due to my sensitivity to sulphur 
dioxyde, I would like to thank all of you who replied either through the list 
or directly.

I finally got the raw chemicals and modified my process to:
- developer
- citric (15gr/l) acid stop bath
- rinse
- Kodak F-9 modified (see below) fixer in 2 baths
- rest of the process

The original F-9 formula is the following:
Water    600ml    Hot water
Sodium Thiosulfate    360gr    crystalline or 230gr anhydrous
Ammonium sulfate    60gr    
Sodium Sulfite (anhydrous)    15gr    
Acetic Acid glacial    13.5ml    
Boric Acid    7.5gr    
Potassium Alum (fine dodecahydrated)    15gr    Do not use anhydrous
Cold water to make    1000ml    
As you can see, it's a hardening formula which I don't need.

The simplified formula I use is the following:
Water    600ml    Hot water
Sodium Thiosulfate    360gr    crystalline or 230gr anhydrous
Ammonium sulfate    60gr    
Sodium Sulfite (anhydrous)    15gr    
Cold water to make    1000ml    
Bob Kiss suggested to add 5gr/l of sodium metaborate as to keep the solution on 
the alkaline side. As I wasn't able to find the metaborate (tried two chemical 
distributors, both were out of stock ...), I started without it, will add it 
later.
The good thing is that, as the dilution of the sodium thiosulfate looks 
endothermic (absorbs heat), the temperature cools down and you can use it 
quickly after. So, no need to prepare it long in advance.

I was also looking for a fast fixer. Fast fixers are normally based on ammonium 
thiosulfate but F-9 is described as being fast *and* based on the more readily 
available sodium thiosulfate.
So I compared the F-9 modified formula to Ilford Rapid Fixer at 1+4 (typical 
film strength) by putting a film leader in each and measuring the time it took 
to clear.
I used of course the same film type from the same lot (from a bulk roll) and 
the temperature of both fixers was identical.
The clearing was just slightly slower, a few seconds, in the F-9, so, from a 
practical point of view, I just keep the same fixing times.
Looks like the ammonium ions coming from the sulfate are making the difference 
but my limited chemical skills do not allow me to be affirmative on this.

For those who tone the prints in selenium, because the fixer is no more acid, 
the risk of stains has gone and there is no  need to wash the prints between 
the fixer and toner, I just put a rinse between them.

I continue to use a washaid (sodium sulfite @ 20gr/l discarded at the end of 
the session) before the final wash as to keep the wash times and water 
consumption at the minimum.

On the smell and sulphur dioxyde side, I'm really happy, my lungs confirmed 
this is the way to go ...
Note that before the non-acid fixer, I tried also to put a rinse between the 
stop bath and an acid fixer and it already diminished the quantity of sulphur 
dioxyde that was released but there was still some coming from the fixer alone.

The next steps on the fixer side are to put in place an efficient and practical 
way of measuring the exhaustion of the fixer and quality of the fixing. I was 
used to use the potassium iodide test (very easy to do) but seen the recent 
"Fixer test vs fixer test" discussion, I'll have to re-think it and try to see 
if I can relate in some ways a more accurate test but more cumbersome (selenium 
test) and the easy potassium iodide test.


Claudio Bonavolta
http://www.bonavolta.ch

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