Test for fixing time

[Matthew Rolfe]

I have been testing for Adox 100 fixing times in Ilford Rapid fix;

- After three minutes in pure fixer the piece of film is almost clear but a very thin cloudy layer refuses to dissolve.

- I give up and remove the piece of film and run it under water. It instantly clears.

Now I have three questions. Firstly: what is the reason for a stubborn cloudy layer that only dissapears when run under water? Secondly: Is this a known characteristic of Adox films? Thirdly/finally: how do you conduct an accurate test when you are never quite sure when it has cleared in the fixer?

[theBDT]

After about two minutes in rapid fix, it should be safe to expose the film to dim light. You can then eyeball/inspect the negative to see if it has cleared. As a rule of thumb, negatives should be fixed for twice the time it takes them to clear.

I, personally, have found that after three minutes or so my negatives are always cleared, so I wait three minutes to turn on lights. Then, I make sure they've cleared, and continue to fix for another three minutes. I imagine that an extra minute or two in the fix isn't going to hurt anything...

[Matthew Rolfe]

I have been doing this test in daylight using unexposed film, just putting a bit in the fixer and watching. I'm always cautious about over fixing, so I run the test. The piece of film must have cleared within the 3 minutes, but it is not until I hold it under water that it is visibly cleared. I would imagine that it is some sort or residue, a bi product of the chemical reaction perhaps?

[jnantz]

are you agitating your film while in the fixer ?

does the white residue stay if you double bath fix it ?

[Matthew Rolfe]

I do agitate in the fixer, I haven't tried double bathing, I will investigate. Thanks.

[jeroldharter]

Something sounds wrong. What is the dilution of the rapid fix? I believe it should be 1:4. With constant agitation, the milky appearance should clear rapidly i.e. within a minute and fixing time should be roughly double the clearing time (perhaps triple with films like TMax).

Maybe the temp is too cold in England now? I assume you don't have a really cold darkroom. Our low temp for tomorrow is -21C.

[Maris Rusis]

I have been testing for Adox 100 fixing times in Ilford Rapid fix;

- After three minutes in pure fixer the piece of film is almost clear but a very thin cloudy layer refuses to dissolve.

- I give up and remove the piece of film and run it under water. It instantly clears.

Now I have three questions. Firstly: what is the reason for a stubborn cloudy layer that only dissapears when run under water? Secondly: Is this a known characteristic of Adox films? Thirdly/finally: how do you conduct an accurate test when you are never quite sure when it has cleared in the fixer?

Pure rapid fixer is no good for fixing film! Ever noticed how heavy a bottle of concentrated rapid fixer is compared to bottle of water? This is because there is a lot of ammonium thiosulphate in there and only a minimum of water. In effect the water has no extra capacity to dissolve anything and this includes the soluble products of the reaction between silver halides and ammonium thiosulphate. For fixer to work water must be added.

This is how I find the clearing time. First I put a drop of diluted (working strength, usually 1+4) fixer on exposed but undeveloped film and leave it there for five or ten minutes. Then I wash the drop off leaving a clear spot on the film. Then the film goes into the fixer being tested until the clear spot matches the rest of the film. The time for this to happen is the "clearing time" and a good and workable tradition is to make the fixing time double this.

[theBDT]

I'm always cautious about over fixing...

Unless you are leaving your film in rapid fix for like 10+ minutes or something, over fixing is not an issue. I would worry more about underfixing than overfixing...

[Matthew Rolfe]

Jerold, The temperature in my darkroom is ok, the fixer is at around 20degrees when diluted. It is getting cold over here, but english people tend to make a lot of fuss over nothing...we have a few inches of snow, -5 to -10 at night time and the whole country is coming to a stand still. Who knows what would happen if we recieved temperatures around -20. :D



Maris, that would make a lot of sense, seing as the water clears the film straight away. And yes now you mention it the bottle of fixer is heavier. I will follow your instructions on how to conduct a 'clearing' test. I haven't used this fixer much before, I now know, thanks.