Black precipitate in my fixer

esbenrossel · Jul 30, 2006

I've studied abroad for six months, so I'm happy as a clam to come home to my room and my darkroom again. However, in my paper fixer a black precipitate has formed a layer on the walls of the container. I normally wouldn't worry about it, but every time I pour fixer in my trays a small amount of black particles follow.

Does anyone know what it is and how I can avoid it in the future? And why didn't my film fixer suffer?

Ian Grant · Jul 30, 2006

Filter the fixer, all that has happened is some of the dissolved silver has deposited itself on the walls of the container. It won't cause any harm and is totally normal

You can use coffee filters to do this.

Ian

pentaxuser · Jul 30, 2006

Ian. I have had this happen in my Nova Quad as well and it worried me - unduly as it would appear from your reply. Presumably the fixer has already been used which is why there are silver deposits there.

At what point( I am thinking of amount) in the formation of the precipitate should the user begin to suspect that the precipitate indicates the fixer is coming to the end of its life.

I noted on another thread that Ryuji has said that fixer replenishment is ineffective and his argument makes sense to me. So its crucial to decide when fixer has been exhausted. Should we simply ignore any black precipitate and rely on information of usage rate, backed up by a fixer test strip or is this precipitate in anything but a minimal quantity the indicator that the fixer is about to be exhausted?

Thanks

pentaxuser

Ian Grant · Jul 30, 2006

The old rule of thumb was to test your fixer by taking the leader from an exposed 35mm film and timing how long it took to clear in the fixer. (Undeveolped obviously)

In practice film fixer can still work with quite high levels of dissolved silver. Fixer replenishment has never been advocated for anything other than mechanised processing.

Actually if the silver precipitates out this will ironically extend the life of the fixer.

This is only true for film processing. Print processing, particularly fibre based papers,requires that the fixer contains far less silver as there are unstable silver/thiosulpahte complexes which are less soluble and can remain in the paper base. This is the reason two bath fixing is advised for archival permanence

Ian

pentaxuser · Jul 30, 2006

Ian Grant said:
The old rule of thumb was to test your fixer by taking the leader from an exposed 35mm film and timing how long it took to clear in the fixer. (Undeveolped obviously)

In practice film fixer can still work with quite high levels of dissolved silver. Fixer replenishment has never been advocated for anything other than mechanised processing.

Actually if the silver precipitates out this will ironically extend the life of the fixer.

This is only true for film processing. Print processing, particularly fibre based papers,requires that the fixer contains far less silver as there are unstable silver/thiosulpahte complexes which are less soluble and can remain in the paper base. This is the reason two bath fixing is advised for archival permanence

Ian

Thanks. My query was related to paper fixer and as he mentioned trays I had assumed that the originator was referring to paper as well.

So in summary is there a test for paper fixer and what if any conclusions can we draw from seeing silver precipitate in paper fixer?

If there is a test then presumably it is also applied to the two bath fix to decide when the first bath needs dumping?

Thanks

pentaxuser

Jim Jones · Jul 30, 2006

I use Edwal Hypo-Check for paper fixer.

reellis67 · Jul 30, 2006

Jim Jones said:
I use Edwal Hypo-Check for paper fixer.

As do I. It seems to do a good job for the paper fixer.

- Randy

Ryuji · Jul 30, 2006

Ian Grant said:
Filter the fixer, all that has happened is some of the dissolved silver has deposited itself on the walls of the container. It won't cause any harm and is totally normal

You don't get black precipitate in paper fixer (usually); you get it in some developers and film fixer.

The black stuff can't be filtered out in the case of film fixer, as they tend to break down to fine particles to go through the filter and come back to bigger form in some time... I'd say just ignore 'em.

I am not sure if some paper can cause the same problem as the film in fixer, but in my experience with several AGFA papers, I see very little visible precipitate in the paper fix.

Those dark stuff appearing in the fixing bath is aggregate form of dye molecules that came off the emulsion and deteriorated. Not harmful to the processing or emulsion anyway.

Metallic silver almost never precipitates in fixing bath. That reaction does not happen in absence of external driving force such as voltage or metals of different ionization potential. Metallic silver is much more common in developer bath, where the developing agents can act as the driving force.

What can sometimes precipitate out in fixer is insoluble silver thiosulfate bromide complex. This is most common in roller transport processing machines. When fixer is not fresh, it can precipitate on the surface of the roller and other places where films can come in contact. It's rare to see it in the tank because the salt will dissolve into the fixer. Anyway, this salt precipitation is VERY rare in manual processing, except that it can occur within the emulsion (sometimes you notice that the film becomes whiter in the middle of fixation, maybe at about 70% of clearing time.) Anyway, this is irrelevant details for most people here.

Again, as summary, I wouldn't worry about colored precipitates in fixer as long as the fixer fixes with reasonable clearing time. In the case of paper, use standard iodide test or use Edwal Hypo Check.

Ryuji · Jul 30, 2006

esbenrossel said:
And why didn't my film fixer suffer?

It's strange that you see this in paper fix and not in film fix. It's usually oppositte. What films/papers do you use??

Ian Grant · Jul 30, 2006

Get your facts right Ryujii.

Silver is deposited on the sides of the fixer container, it happens in any fixer that is laden with dissolved silver. Much of this falls to the bottom of the container.

Try a ferrycyanide bleach it will all be converted bach to Silver Halogen salt, it most certainly isn't "dye molecules that came off the emulsion"

Ian

Ryuji · Jul 30, 2006

Ian Grant said:
Silver is deposited on the sides of the fixer container, it happens in any fixer that is laden with dissolved silver. Much of this falls to the bottom of the container.

This usually doesn't happen, at least in common ammonium thiosulfate fixers, unless you put some non-silver metal, chemical reducing agents or electric current in the solution. I've never seen it in my fixers.

If you contaminate your fixer with developer, metallic silver may come out. It's a common problem and it's the reason why dichroic fog can happen this way.

On the other hand, if metallic silver can precipitate in the fixer solution while it's sitting in a bottle doing nothing, that's a new technology that allows "self rejuvenating fixer" that can be used forever without electrolytic silver recovery system!

Again, the kind of things that can precipitate in fixing bath are aggregated dye molecules (which may be bleached by oxidizing agents like ferricyanide, but it is much lighter than metallic silver so the sediment can be easily disturbed, unlike in the case of metallic silver), elemental sulfur (in case of acid fix), and some other silver salts but not metallic silver.

Try a ferrycyanide bleach it will all be converted bach to Silver Halogen salt, it most certainly isn't "dye molecules that came off the emulsion"

Just because they disappear in ferricyanide, it doesn't mean they are silver. A lot of things disappear in this very powerful oxidizing agent. What did you do exactly to determine that it is silver?

Also, ferricyanide destroyes thiosulfate, so if you add ferri to exhausted fixer, you get some silver compounds that are separated from stable silver-thiosulfate complex form. Testing for this kind of things must be done very carefully.

If you do some numerical simulation using stability constants, it'll be obvious that the most stable silver compound in the usual fixer solutions is silver-thiosulfate complex species (even in ammonium thiosulfate fixer) and they are not going to come out of the solution, again, in absence of external driving force. Even "exhausted" fixer has a very large excess of thiosulfate and these species are stable.

Ian Grant · Jul 30, 2006

Try reading your own post.

I'll leave you to your ineptitude

Ian

Ryuji · Jul 30, 2006

Ian Grant said:
Try reading your own post.

I'll leave you to your ineptitude

Ian

Ian, I don't know what kind of comment this is, but I'll give it back to you and I'm done with it.

dancqu · Jul 30, 2006

esbenrossel said:
I've studied abroad for six months,...
However, in my paper fixer a black precipitate
has formed a layer on the walls of the container.
And why didn't my film fixer suffer?

Six months plus how many more was that fixer
in the container? How much use had it seen prior
to your departure? What sort of container? Was
the container full to the brim?

Likely that pre-used fixer, after maybe a year of
mostly sitting in a bottle, has oxidized and is shot.
That black precipitate, I'd think, silver sulfide. Dan

esbenrossel · Jul 30, 2006

Thank you all for answering.

For those wondering the fixer is Kodak General Purpose Hardening Fixer. I mostly use Agfa fiber and occasionally Ilford rc paper. Films used are fp4+, hp5+, foma 100, tmax 100 and tri-x.

It was a fairly used solution when I left home, but certainly not dead as it still cleared film within a minute yesterday. The black layer is pretty thick (like a thick paint layer) and some particles come loose when I pour the fixer in my trays. The black stuff didn't respond to bleaching with LARGE excess of ferric cyanide and so far fresh fixer hasn't been able to remove it either.

I just wanted to check if anyone had experienced the same problem and knew of a solution. Mine will be getting a new container and making up some fresh fixer. Filtering without suction is not for my patience (and only in the lab do I have that luxury).

pentaxuser · Jul 31, 2006

Esbenrossel.

If you are asking about how to clear the black deposits from the inside of your paper fixer container, then I can say that after draining the fixer slot in my Nova Quad slot processor, I have filled it with dilute household bleach at about 1:15 ratio and have left it overnight then cleaned it with a bottle brush. This has removed the black deposits which stick to the the side which are then flushed out with water. As the Nova is a hard plastic material then presumably the same should work with another plastic or glass container.

As Ian has said and it apppears to be one point on which he and Ryuji agree, the black particles, suspended in the fixer, whatever they are, are harmless per se and can be filtered through a coffee filter paper.

What then counts is whether the paper fixer, duly filtered, and now clear contains too much silver to be effective in fixing paper.

Two subscribers have suggested independently of each other that the use of Edwal test strips will determine whether the fixer is still good.

I have been following a number of threads on fixer and it seems that there is no simple visual way of checking paper fixer or a no cost way such as there is for film.

So unless anyone knows differently, you have to test paper fixer by a recognised chemical means such as Edwal test strips.

There may be alternatives to Edwal. I don't know if these are available in the U.K. or rest of Europe.

Any information on this would be useful as it seems that checking chemically and then dumping when exhausted seems the best way for paper fixer rather than replenishment which as Ryuji point out results in a build up of fixer which cannot be removed by simple replenishment.

pentaxuser

Thomas Bertilsson · Jul 31, 2006

I would say if it bothers you, dump it, and mix new fixer. It's an interesting question, but by comparison, fixer is cheap. Much cheaper than any uncertainty and worry about what that black sludge might contain.

- Thom

Ryuji · Jul 31, 2006

pentaxuser said:
As Ian has said and it apppears to be one point on which he and Ryuji agree, the black particles, suspended in the fixer, whatever they are, are harmless per se and can be filtered through a coffee filter paper.

I agree it is harmless but I don't know if the particular black stuff can be removed through paper filter. In many cases, the blackened dye aggregate I found in my fixer break up into fine particles and go through the paper filter. After some time, they stick to each other to make bigger black stuff. I just ignore them.

Edwal Hypo Check is not a strip. It's a solution of potassium iodide. You can make your own KI solution according to Kodak formula (and I've used it as well).

As a way to remove general black stain from trays and others, a classic way is to use dichromate bleach. But you can use acid thiourea solution. Acid thiourea solution is a very powerful bleach that dissolves metallic silver and silver sulfide. It may be a bit slow so leave it on the dirty area for some time before cleaning. You can use sulfuric, sulfamic, etc. as the acid.

Photo Engineer · Jul 31, 2006

Generally, as fixer ages, it forms sulfur compounds which no longer form soluable complexes with silver. Therefore, a bad fixer that is laden with silver complexes will gradually produce a 'silver mirror' effect on the surface of the container with some sulfur colloid suspended in the liquid and sometimes some hydrogen sulfide. Sometimes, the 'silver mirror' will break up and form a black deposit on the bottom of the container.

I suggest the use of the potassium iodide fixer exhaustion test. You have to practice to gain skill with it, but it is quite good after you learn how to use it.

PE

dancqu · Jul 31, 2006

esbenrossel said:
Thank you all for answering.
The black layer is pretty thick (like a thick paint layer)...
The black stuff didn't respond to bleaching with LARGE
excess of ferric cyanide and so far fresh fixer hasn't
been able to remove it either.

Why ferric cyanide did nothing I don't know. None of
the posts following yours shed any light. I was expecting
some explanation.

Pentaxuser brings into this give-and-take some matters
of concern. A taken for granted testing method is a blaring
example of ignoring suggested maximum levels of silver for this
or that purpose. The FT-1 test uses potassium iodide as an
indicator of silver levels. There seems to be no agreed upon
method of conducting the test or exactly how to interpret
the results. I think that a shame. The test should have
great potential as it is a titration and ought to be
quantified.

I worked on that some a few years ago. One thing I
did find out was that at very low levels of silver, perhaps
archival, the precipitate is so fine and disbursed as to make
it difficult to detect an end point.

If one wishes to check for silver in the print use the
ST-1 test. A sulfide is used as a spot check. Dan

Photo Engineer · Jul 31, 2006

dancqu said:
Why ferric cyanide did nothing I don't know. None of
the posts following yours shed any light. I was expecting
some explanation.

Pentaxuser brings into this give-and-take some matters
of concern. A taken for granted testing method is a blaring
example of ignoring suggested maximum levels of silver for this
or that purpose. The FT-1 test uses potassium iodide as an
indicator of silver levels. There seems to be no agreed upon
method of conducting the test or exactly how to interpret
the results. I think that a shame. The test should have
great potential as it is a titration and ought to be
quantified.

I worked on that some a few years ago. One thing I
did find out was that at very low levels of silver, perhaps
archival, the precipitate is so fine and disbursed as to make
it difficult to detect an end point.

If one wishes to check for silver in the print use the
ST-1 test. A sulfide is used as a spot check. Dan

Silver sulfide often forms in decomposing fix. Silver iodide also forms.

These are particularly resistant to re-solution in fresh fixer, and are not affected at all by oxidants such as ferricyanide.

The formation of silver sulfide is the result of decomposing acidic fix which forms hydrogen sulfide, and since silver sulfide is very insoluable and black, it precipitates out of the fixer.

PE

Ronald Moravec · Jul 31, 2006

Don`t use 6 months old and get rid of the storage bottle before it contaminates the next batch.

Same thing happens to film fix, except the particals stick to the next film. Of course you can learn to spot prints and just keep using it to capacity. I use mine up on test prints.

Bounty Paper towels quartered and cotton wool make the best filter combination, but it is not 100%. Coffee filters are not even close.

pentaxuser · Aug 2, 2006

P.E. and Dan. A couple of questions based on the last few posts:

1. What are the difficulties in interpreting the potassium iodide test?
2. What are the FT-1 and ST-1 tests respectively?
3. If one should use the ST-1 test to check for silver in the print, is this the potassium iodide test which takes practice to be competent at or something more straightforward ?

Thanks

Slightly confused of Daventry

pentaxuser

Photo Engineer · Aug 2, 2006

pentaxuser said:
P.E. and Dan. A couple of questions based on the last few posts:

1. What are the difficulties in interpreting the potassium iodide test?
2. What are the FT-1 and ST-1 tests respectively?
3. If one should use the ST-1 test to check for silver in the print, is this the potassium iodide test which takes practice to be competent at or something more straightforward ?

Thanks

Slightly confused of Daventry

pentaxuser

There are 3 tests involved:

KI added to used fixer will cause little or no precipitate if the fixer is good, but a heavy yellow precipitate if the fixer is bad. The trick comes in gaining the experience to distinguish all of the gradients in between.

Na2S (sodium sulfide) solution added to film or paper gives a black spot test for the presence of silver halide remaining behind in the coating after fixation. This will be a dense spot if the fixer is improper either by virture of time, exhaustion, or dilution. There is no spot if fixation is proper.

AgNO3 + acetic acid (Acidified silver nitrate solution) is added to a film or paper and gives a yellow spot if there is retained hypo. This test is very sensitive and Kodak makes (or made) a strip density test patch to compare your prints to for judging quality of your wash.

PE

Mark Pope · Sep 27, 2006

pentaxuser said:
So unless anyone knows differently, you have to test paper fixer by a recognised chemical means such as Edwal test strips.

There may be alternatives to Edwal. I don't know if these are available in the U.K. or rest of Europe.
pentaxuser

Tetenal make a fixing bath test kit. It's available from Silverprint: http://www.silverprint.co.uk/dark36.html. I use this kit. You have a paper strip with a couple of patches that you immerse in the fixer. After a minute, you compare the colours of the patches against two colour charts on the container. One gives you the pH of the solution and the other the amount of silver in the fixer. The data sheet gives the thresholds at which the fixer should be discarded.
It only takes a few minutes to check before starting a printing session.
I think Mr Cad stock Edwal products. Not sure if the fixing kit is one of them though.

Black precipitate in my fixer

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