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Indicator Fixer

cliveh

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35mm RF
If it is possible to buy an indicator stop bath, why don't manufacturers make an indicator fixer, or is this not possible?
 
Simplified answer: Fixer is exhausted when silver content exceeds fixing capability, and fixing times become excessively long. After that, no fixing at all and you get prints or film that turns dark from under fixing. IIRC, there's a test solution for that, but I've never used it as I rely on Mfg recommendation .
 
Rick A said:
Simplified answer: Fixer is exhausted when silver content exceeds fixing capability, and fixing times become excessively long. After that, no fixing at all and you get prints or film that turns dark from under fixing.
Click to expand...

So is it not possible to put a colour indicator into the chemistry to show when silver content exceeds fixing capability?
 
IDK about making a fixer that turns color when nearing exhaustion, but it's pretty easy to keep an eye on your fix. You can save the leader from your roll of film and drop it in the fix. It should turn clear in about 1 min. with good fixer.

Edwal makes a fixer test solution and when you put a drop from the bottle into the fix, it will turn cloudy when near the end of its life.
 
cliveh said:
So is it not possible to put a colour indicator into the chemistry to show when silver content exceeds fixing capability?
Click to expand...

AFAIK, all the common colour indicators respond to changes in acidity (ph). ph is a determinant of the health of stop bath, but is not related to the health of fixer.

And by the way, silver concentration is one of two measures of the capacity of fixer. You can have fixer that is not yet saturated with silver but is still unable to do its job - due to factors like dilution and loss of chemical capacity.
 
There are two chemicals that affect a fixer regarding exhaustion. One is silver content and the other is iodide content. One, the other or both build up to intolerable levels and shut down the fixer. There are no color tests as there are in stop baths.

So, I said NO and I mean NO. AFAIK, no one has ever achieved this. So, go ahead and do some R&D, become a hero and patent it and then reap your rewards. But, I say you will find nothing that works.

PE
 
Sounds to me like a pAg indicator and a pI indicator are needed. Dunno if any such things exist. Easier to just test your fixer, I think.
 
pAg and pI indicators exist, and they are called Multimeters, but in the presence of hypo, they tell you nothing as they only function well in the absence of silver halide solvents.

PE
 
cliveh said:
Why not?
Click to expand...

because fixer exhaustiois caused bythe accumulation of silver salts in the fixer.as soon as the fixer contains more than 0.5g of silver/ liter, it should be replaced for archival processing.with two-bath fixing, the first fix can have up to 2g silver/ liter but needs to be folloed by a fresh 2nd bath.
 
cliveh said:
So is it not possible to put a colour indicator into the chemistry to show when silver content exceeds fixing capability?
Click to expand...

No The pH indicators are weak acids or bases and the color change is dependent on the removal or addition of a hydrogen ion to the molecule and its subseguent structural re-arrangement. The difference in the two structures accounts for the color difference.

Fixer test solutions are not particularly accurate either as it is hard to interpret the results.

The best and most reliable method for tracking fixer exhaustion is to keep track of the number of in2 of film and paper passed thru it. Do not exceed the manufacturers recommendation. Doing this and using a two bath system makes for a very reliable fixing regime.
 
Last edited by a moderator:
I never heard of indicator fixer. I use hypo test.
 
Let's safely take what PE said for granted it can't be doneI don't know anybody who would know better than him; use the manufacturer's recommendation andjust count your rhroughput to avoid fixer exhaustion.
 
Henpe, those strips test for pH (possible if you know the starting pH of your fix), and Silver content. However, Silver activity depends on too many things to make this reliable. For example, a fix used for paper may give a less reliable test as it then contains more Silver Bromide and Chloride than a film would and thus the color would be different. Silver Iodide is dark red to black in some cases, while Silver Chloride is white. The halide present in the fix can participate in the final color.

Also, whether the fixer contains Sodium Hypo or Ammonium Hypo influences capacity. This also changes the color as well.

Thus, you have to know too many things to figure out what the color means (if anything). With the pH of a stop it is one color change, and that is it!

So, your test strips are something that can be made reliable, but they would require a fixed workflow and lots of testing and verifying.

PE
 
Compared to film, cameras and lenses, hypo is cheap. Why risk your negatives and prints? Buy a small bottle of hypo test and use it.
 
PE, this may be but just for the record,Tetenal claims that these strips test for pH andsilver content.I preferred them over the iodide testand stopped using the paperfix after they indicated 0.5-1.0 g silver/ liter;worked for me in combination with two-bath fixing.
 
Ralph, I am sure that the Silver indicator works, but I believe that it is inaccurate and takes a while to get used to as results vary according to usage. I have no doubt that the pH test works. After all, that is a simple high school experiment.

A simple film clip test works best for me.

PE
 

I am thinking about running ICP analysis on my fixer for determination of its longevity. This might be the best way, plus our ICP technician needs more work to do at my company.
 
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