To the chemistry experts on the forum

snusmumriken · May 11, 2022

I'm curious to know about the chemistry of fixer and selenium toner residues. I must stress at the outset that neither are a problem to me, I don't lose any sleep over them - I'm just curious.

Where fixer crystallises out (e.g. around the neck of the bottle), it creates a pale yellow encrustation that will not dissolve in water, nor in a potassium permanaganate/sulphuric acid cleaning solution. What is the encrustation (chemically), and what would actually shift it? (I use rapid fixer these days, but the same used to happen with regular hypo.)
The trays I use for selenium toner and for a water rinse after toning acquire pinky-grey stains on the sides where splashes have occurred. Again, these are seemingly impossible to remove. No such stains occur where the tray has been fully covered by the toner or water bath. I rinse trays assiduously straight after use, including the sides. I don't care that my trays are stained - that goes with the territory - but I am curious about what chemical change has occurred here.

Any ideas?

Donald Qualls · May 11, 2022

The yellow encrustation is probably elemental sulfur. The only thing I know that's reasonably accessible and will dissolve it is carbon disulfide.

Fixer forms sulfur as the thiosulfate and sulfite in the solution break down with age and oxidation. This starts with sulfur dioxide, giving the characteristic odor of old fixer; I don't know the mechanism that causes this to reduce to elemental form, but that's known to be (in colloidal form) the culprit when fixer gets a cloudy appearance coupled with a sulfurous odor.

Can't help you with the selenium, though I suspect it's a similar effect.

greg zinselmeier · May 11, 2022

been there! about a year ago, maybe nine months ago. i too tried my best to clean my trays, from Selenium toner. I got a few tips I can pass along.

first about the yelllow stain, What type of material is your bottle made from? what type of plastic, or . . .? I think the complex salts are interacting with the type of plastic you use.

The crust has residual salts of variety of compounds made from fixing your fim and paper. there is dissolved silver in your fix along with other elements. potentially, a wide variety of salts along with the Hypo. Which one (s)(compound) is causing the plastic to stain? IDK.

the Selenium toner, I too have had issue with. My dedicated tray has a black bottom from toning Foma Retrobrom. I think it is because of the Iodine in the paper, that causes this form to percipitate out, Because it does not do that with Fomabrom 111. and there is HYPO in selenium toner.

After toning paper, I strain through a coffee filter. ( i got this tip from another Apuger) and that seems to eliminate the vast majority of percipitant. the color neutralizes by the next day.

Cuprocene · May 11, 2022

I would try oxidizing the sulfur to a sulfate with bleach. It might be slow, but the sulfate should come off in hot water. Pinky-grey could be a mixture of pink sodium selenite and gray selenium-- bleach could be another good choice there.

snusmumriken · May 11, 2022

greg zinselmeier said:
been there! about a year ago, maybe nine months ago. i too tried my best to clean my trays, from Selenium toner. I got a few tips I can pass along.

first about the yelllow stain, What type of material is your bottle made from? what type of plastic, or . . .? I think the complex salts are interacting with the type of plastic you use.

The crust has residual salts of variety of compounds made from fixing your fim and paper. there is dissolved silver in your fix along with other elements. potentially, a wide variety of salts along with the Hypo. Which one (s)(compound) is causing the plastic to stain? IDK.

the Selenium toner, I too have had issue with. My dedicated tray has a black bottom from toning Foma Retrobrom. I think it is because of the Iodine in the paper, that causes this form to percipitate out, Because it does not do that with Fomabrom 111. and there is HYPO in selenium toner.

After toning paper, I strain through a coffee filter. ( i got this tip from another Apuger) and that seems to eliminate the vast majority of percipitant. the color neutralizes by the next day.

My fixer bottles are glass, so I don't think a reaction is likely. The encrustation is presumably a decomposition or oxidation product.

I do filter my selenium toner before each use, and then rinse the (glass) toner bottle which as a result stays nice and clean. The greyish-white precipitate I understood to be silver selenite, though that could be wrong. I think what's happening in the trays is different.

Cuprocene said:
I would try oxidizing the sulfur to a sulfate with bleach. It might be slow, but the sulfate should come off in hot water. Pinky-grey could be a mixture of pink sodium selenite and gray selenium-- bleach could be another good choice there.

Thanks for that insight! I'll give bleach a try.

Doremus Scudder · May 11, 2022

The yellowish fixer precipitate is, as mentioned, most likely elemental sulfur. You can minimize this by not over-using your fixer or storing a working solution for long periods of time. I like to use fixer one-batch, i.e., I just mix enough for the amount of film I have. When printing, too, I try to print enough to use the fixer up enough I can discard it (I take mine for silver recovery at a local photo lab).

Sodium selenite is the active ingredient in your selenium toner. It's red, hence the print tone shifting to the red and the red stains from drips that dry. These can be hard to clean when dry, so get in the habit of wiping things down right away before they've had a chance to dry.

The black stains on your toner tray are silver selenite most likely if you transfer your prints directly from fixer to toner like I do. Some silver thiosulfates from the print dissolve out into the toning solution and then combine with the selenium toner. This seems to want to coat tray surfaces. Bleach and a good scrubber sponge are your friends here.

Best,

Doremus

greg zinselmeier · May 11, 2022

all good info for me too!!

To the chemistry experts on the forum

snusmumriken

Donald Qualls

greg zinselmeier

Cuprocene

snusmumriken

Doremus Scudder

greg zinselmeier

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