How long does unused fixer stay usable?

"Michael A. Covington"
wrote in
message ...

"Timo Geusch" wrote in message
...
Michael A. Covington was seen penning the following ode
to ... whatever:
The bottom line is that 2 minutes just isn't a long
enough fixing time.
Note that Tri-X has been re-engineered recently. Were
you using one of
the
new films (320TXP or 400TX, with the numbers in front
of the letters) or
one
of the old ones (TX or TXP)?

400TX. I'll take you comment about fixing time on board
and make sure
that I'll fix it properly the next time.

OK -- now we know exactly what got you. 400TX is not the
same old Tri-X
Pan. Although photographically similar, it is a new
product with (I think)
a harder emulsion. So a fixing time that was (barely)
adequate for TX might
well be too short for 400TX.

Mystery solved!

Now as for the development times for 400TX... there are
lots of open
questions there!

The emulsion hardness should not significantly affect
fixing time. Gelatin hardness is really a measure of how
much it swells and softens at higher temperatures. The
diffusion rate is not directly related to this property.
Tri-X or 400TX is slow to fix, perhaps because it has a lot
of silver iodide in the emulsion. Silver iodide is resistant
to fixing. This is also why T-Max and other tabular grain
films tend to take longer to fix out than other films. The
usual rule of thumb is to fix for twice the clearing time
but for these films three times the clearing time is
probably closer to the mark. Ammonium thiosulfate ("rapid
fixer") is less sensitive to dissolved iodide than sodium
thiosulfate fixer so it is advantageous for modern films of
all types, but especially hard to fix films like Tri-X,
T-Max, Delta, and Fuji Acros.
The ability of a fixing bath to convert the insoluble
silver halide to a soluble form depends on how much silver
is dissolved in it. In order to complete the complex chain
of reactions which make the halide soluble there must be an
excess of free thiosulfate ions. As the fixer works more and
more silver is dissolved in it all bound to thiosulfate. At
some point the fixer will still clear the film but will not
completely remove the unused halide. The halide residue will
eventually decompose and generate a stain and may attack the
silver image. So, complete fixing is important for long
image life. A two bath fixing system tends to concentrate
the dissolved silver in the first bath leaving a lot of free
thiosulfate in the second bath to scavenge any remaining
halide and make it soluble.
The life of an unused fixing bath solution depends on the
stability of the constituents. Acid fixer depends on the
sulfite to keep the acid from decomposing the thiosulfate.
After long enough this decomposition will occur, usually
resulting in elemental sulphur being deposited in the
container. The sulfite is oxidised by air, becoming sulfate.
Sulfate is not capable of protecting the thiosulfate from
the acid. Non acid fixing baths probably have a longer shelf
life but sulfite is still necessary to prevent staining from
carried over developer. I think it still protects the
thiosulfate. Again, it will eventually oxidize. Kodak gives
two months as the life of mixed working solution fixer.
Kodak's numbers are always conservative; they want the stuff
to work. Fixer probably lasts six months but I wouldn't
count on longer. If any cloudiness appears the stuff should
be tossed.
I don't know the actual shelf life of un-opened rapid
fixer concentrate, but have had bottles of Kodak Rapid
Liquid Fixer decompose after a couple of years. The plastic
bottles are not completely impervious to air so eventually
the stuff will die. It might last longer in glass, who
knows.
Fixer should be considered an expendible. It is too
important to permanent results to pinch pennies with it.

Why not test it before use rather than speculating?

"Richard Knoppow" wrote in message
ink.net...

"Michael A. Covington"
wrote in
message ...

"Timo Geusch" wrote in message
...
Michael A. Covington was seen penning the following ode
to ... whatever:
The bottom line is that 2 minutes just isn't a long
enough fixing time.
Note that Tri-X has been re-engineered recently. Were
you using one of
the
new films (320TXP or 400TX, with the numbers in front
of the letters) or
one
of the old ones (TX or TXP)?

400TX. I'll take you comment about fixing time on board
and make sure
that I'll fix it properly the next time.

OK -- now we know exactly what got you. 400TX is not the
same old Tri-X
Pan. Although photographically similar, it is a new
product with (I think)
a harder emulsion. So a fixing time that was (barely)
adequate for TX might
well be too short for 400TX.

Mystery solved!

Now as for the development times for 400TX... there are
lots of open
questions there!

The emulsion hardness should not significantly affect
fixing time. Gelatin hardness is really a measure of how
much it swells and softens at higher temperatures. The
diffusion rate is not directly related to this property.
Tri-X or 400TX is slow to fix, perhaps because it has a lot
of silver iodide in the emulsion. Silver iodide is resistant
to fixing. This is also why T-Max and other tabular grain
films tend to take longer to fix out than other films. The
usual rule of thumb is to fix for twice the clearing time
but for these films three times the clearing time is
probably closer to the mark. Ammonium thiosulfate ("rapid
fixer") is less sensitive to dissolved iodide than sodium
thiosulfate fixer so it is advantageous for modern films of
all types, but especially hard to fix films like Tri-X,
T-Max, Delta, and Fuji Acros.
The ability of a fixing bath to convert the insoluble
silver halide to a soluble form depends on how much silver
is dissolved in it. In order to complete the complex chain
of reactions which make the halide soluble there must be an
excess of free thiosulfate ions. As the fixer works more and
more silver is dissolved in it all bound to thiosulfate. At
some point the fixer will still clear the film but will not
completely remove the unused halide. The halide residue will
eventually decompose and generate a stain and may attack the
silver image. So, complete fixing is important for long
image life. A two bath fixing system tends to concentrate
the dissolved silver in the first bath leaving a lot of free
thiosulfate in the second bath to scavenge any remaining
halide and make it soluble.
The life of an unused fixing bath solution depends on the
stability of the constituents. Acid fixer depends on the
sulfite to keep the acid from decomposing the thiosulfate.
After long enough this decomposition will occur, usually
resulting in elemental sulphur being deposited in the
container. The sulfite is oxidised by air, becoming sulfate.
Sulfate is not capable of protecting the thiosulfate from
the acid. Non acid fixing baths probably have a longer shelf
life but sulfite is still necessary to prevent staining from
carried over developer. I think it still protects the
thiosulfate. Again, it will eventually oxidize. Kodak gives
two months as the life of mixed working solution fixer.
Kodak's numbers are always conservative; they want the stuff
to work. Fixer probably lasts six months but I wouldn't
count on longer. If any cloudiness appears the stuff should
be tossed.
I don't know the actual shelf life of un-opened rapid
fixer concentrate, but have had bottles of Kodak Rapid
Liquid Fixer decompose after a couple of years. The plastic
bottles are not completely impervious to air so eventually
the stuff will die. It might last longer in glass, who
knows.
Fixer should be considered an expendible. It is too
important to permanent results to pinch pennies with it.

"Pieter Litchfield" wrote

Why not test it before use rather than speculating?

Why not throw it out after each use? I've found that very dilute
fixer is nearly as fast as full strength. Used so it is not wasted.
For now and then darkroom use keep a bottle of sodium thiosulfate
at hand and mix what is needed at time of use. Nothing need be
added. The solution is very slightly acid.
Keep the lid on tight and that sodium thiosulfate should be good
for many years. Dan