Weird "toner" made with TF-4 fixer and oxalic acid?

So today in a variety of lith printing formulation experiments (read: failures) I decided to attempt to remove what appears to be hydroquinone stain by using oxalic acid (sulfite didn't work, but maybe acid would strip it, and oxalic acid was what I could find quickly). However, I had just taken the print out of my (well used) TF-4 fixer and didn't really think about washing it first since it was ruined anyway. I poured a tiny bit of 5% oxalic acid solution onto the print and where I poured a very purple tone came up. This also surprisingly did remove the yellow staining from the unexposed border and only changed the tone on where there was an image. I decided to try this on a few different bad prints I had on hand. Oxalic acid on its own did nothing to any print. If I dripped a bit of fixer and then the oxalic acid onto it though, it worked. Note I did no bleaching of these images and the color intensified slightly with washing, it did not wash out over 1 hour with running water. Results:

* Ilford MGV normal print -- changed image tone to reddish brown, like sepia
* Ilford MGFB normal print -- changed image tone to reddish brown, but unlike with the RC paper it produced a subtle reddish tint to whites (color difference also could've been due to this print already being fairly well washed)
* Ilford MGFB lith print -- removed yellow staining (restoring borders to white) and turned a very deep purple color, like a fully selenium toned print. Also intensified the image quite noticeably
* Arista.EDU Ultra FB lith print -- removed yellow staining, intensified image slightly and gave a distinctly blue tone to the image and slightly changed blacks to a very cool brown. Reminds me of a fully gold toned print.

Also, note that when doing this the sulfite in TF-4 will break down in acid and produce sulfur dioxide gas that is quite irritating and very unhealthy. If a drop of TF-4 is put into oxalic acid it produces a white precipitate.

Anyway, I'm trying to make sense of what is happening here and if there is someway to exploit it, and more importantly, if it's a stable "toning" method that might be possible. It seems plausible that neutralizing TF-4 may produce sodium sulfide, ie, sepia toner, but sulfide does nothing if the print isn't bleached first. It also never produced the blue and purple colors like I've seen. My fear is that it might be creating silver oxalate, which is a sensitive explosive. The small amount within a print is nothing to worry about, but it would definitely mean it's not archival. Anyone with enough chemistry knowledge here to take a guess at what could be happening? Also I'm not sure if the acid being oxalic is important or if TF-4 neutralized with any acid would have a similar effect. Unfortunately didn't have time to test it really.

Silver Oxalate is not overly insoluble, therefore you could easily and quickly verify/disprove this theory by refixing such a blue test clip. I have seen the weirdest colors with chromoskedasic prints, so it may well be silver.

Rudeofus said:

Silver Oxalate is not overly insoluble, therefore you could easily and quickly verify/disprove this theory by refixing such a blue test clip. I have seen the weirdest colors with chromoskedasic prints, so it may well be silver.

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I did try refixing, it made no difference in color at all. I also tried testing if the compound was explosive by simply putting a fire on the emulsion of one of the dried waste prints. No reaction at all, so definitely not silver oxalate

I did more testing also with a proper full bath of oxalic acid. When putting some of the TF-4 fixer into the bath it'll produce a white precipitate that turns yellow as more Tf-4 is added. The solution in this state is active as a toner. It seems to turn some tested lith prints either purple or brown and normal prints blue or red. Normal prints can exhibit some split toning with shadows and blacks intensifying, midtones going a brownish purple, and highlights blue.

Description of this print:

Ilford Warmtone FB first-pass lith printed in ModernLithC1 prototype formula.

After fixing it was toned by an experimental method of dunking the print directly from the (well used TF-4) fixer into a strong oxalic acid bath, causing the bath to go white with precipitate and become quite smelly. Before toning the print was fairly neutral tone with a bit of green olive colors. After toning it turned to a bright red color, then when dunked into water and rinsed the print emitted the distinct "burning match" smell of sulfur dioxide and quickly went to this very interesting brown color that intensified slightly with more rinsing and the overall density of the print seemed to increase. No idea if it's archival, but I like it.

Sounds like it could be essentially a more rapid version of the hypo alum fixer, with the thiosulfate in the fixer becoming a sulfur donor. The mechanism is likely different.
What you said about blue and purple tones appeals to me, but it isn't visible in the example print. Any examples of that tone as well?

One thing, which would greatly encourage other people to investigate this, would be to know whether this is specific to Oxalic Acid and TF-4 fixer. I wonder, whether this can be replicated with standard rapid fixer and/or with any strong acid like Sodium Bisulfate or battery acid.

Well, just did a little experiment with fuji c41 fixer dropped into a weak solution of sulfuric acid. The solution turns milky yellow and ample amounts of SO2 are formed (I had to move the tray outside quickly). After about 10 minutes I don't see much toning action going on (maybe a little) suggesting the thiosulfate simply breaks down, elemental sulfur is being formed but no very active sulfur toning compounds. I'll let it sit for a while and wash the test strips and compare them to untreated ones.

This is one of those experiments that should be done outdoors or at least with AMPLE ventilation present.

koraks said:

Well, just did a little experiment with fuji c41 fixer dropped into a weak solution of sulfuric acid. The solution turns milky yellow and ample amounts of SO2 are formed (I had to move the tray outside quickly). After about 10 minutes I don't see much toning action going on (maybe a little) suggesting the thiosulfate simply breaks down, elemental sulfur is being formed but no very active sulfur toning compounds. I'll let it sit for a while and wash the test strips and compare them to untreated ones.

This is one of those experiments that should be done outdoors or at least with AMPLE ventilation present.

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In my experience, some papers won't have much color until after rinsing

Also, this is an example of the blue and purple color possible. Another lith print, but on Ultra.EDU Ultra RC paper. Originally was fairly neutral tone

Well, I left those strips in the solution for about 45 minutes after which they were thoroughly sepia toned. There was also a buildup of aulfur sludge on the prints and the trays, but it wiped off the emulsion very easily.

The tone is quite attractive on neutral paper (one of the test strips was fomabrom 111). Regular sepia, without the seemingly inevitable yellow hint I get with thiourea toner.

Too bad about the SO2, as this basically seems a somewhat faster approach to a hypo toner, but also with its inherent disadvantage of not being able to tone indoors comfortably.

With closer examination of the prints, the sulfur sludge is definitely a problem. I rinsed these prints extremely well under running water and still got a pretty significant amount. It can probably be wiped off while wet with a damp cloth or something. The sludging will give a slight yellow cast to the image if not wahsed off (along with a powdery appearance) Of greater concern though is that some prints had iron rust contamination embedded into the emulsion. I'm not sure if this is some reaction with the minute amounts of iron in my tap water, or if there is some contamination in my trays (I did iron based experiments several months ago). The threads of iron begin as being pretty much invisible, but after dry they oxidized to form rust orange fibers. Based on previous experience with this problem, it can't be washed out or removed and will turn blue if dunked into a ferrocyanide bleach.

To me, 45 minutes seems like a very long time. I think the longest I did toning was 5 minutes, but maybe if I had toned for a very long time I would've converted the blacks of the image to sepia tone. I definitely the overall color spectrum a bit better than normal sulfide sepia toning, and rather than removing density by bleaching it, it seems to keep the same density or slightly increase density.

In my little experiment toning seems to have gone pretty much to completion resulting in some loss of density across the tonal scale. The blacks are a very deep brown now. It's a pleasant tone for sure and it would work quite well for some images.

@earlz: I did check the colors of this print with GIMP, and the color of these sky scrapers is plain red. I did do a reference measurement of the print borders, too:

• print border: R = 229, G = 225, B = 233, that's actually a tiny bit purple
• right most sky scraper: R = 209, G = 197, B = 196, that's plain red
• dark windows of right most sky scraper: R = 184, G = 172, B = 171, that's plain red
• left most sky scraper: R = 223, G = 212, B = 213, that's plain red
• bright part of the trees to the left: R = 201, G = 179, B = 172, that's plain red, with a tinge of orange

Rudeofus said:

@earlz: I did check the colors of this print with GIMP, and the color of these sky scrapers is plain red. I did do a reference measurement of the print borders, too:

• print border: R = 229, G = 225, B = 233, that's actually a tiny bit purple
• right most sky scraper: R = 209, G = 197, B = 196, that's plain red
• dark windows of right most sky scraper: R = 184, G = 172, B = 171, that's plain red
• left most sky scraper: R = 223, G = 212, B = 213, that's plain red
• bright part of the trees to the left: R = 201, G = 179, B = 172, that's plain red, with a tinge of orange

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One of the things throwing this off is iphone picture color balance is kinda crap, and that I didn't notice until after that it had a layer of yellow scum from the sulfur. Wiping it off a bit revealed much cooler tones. When the print was wet this scum was transparent. I'll have to rewash the print at some point and do a proper flatbed scan of it. It's hard to replicate exact A-B results since I only get the cool colors from lith prints, and not always even on the same paper. The blue color appears to come up the most when yellow staining is present (I believe a combo of hydroquinone staining and general fog). Either way, the SO2 problem is real and I don't have a well enough ventilated space to really feel safe (or at least not highly annoyed) to do much more with it. I expect it's basically a hypo alum type toner accelerated by the bleaching and reducing effect of SO2 in solution. I suspect the blue color is not from sulfide conversion, but rather from some plating effect. I've also noticed afterwards that some prints have a very subtle yellow stain that does not wash off. Either way, look forward to hearing back from people who want to replicate this and do have enough ventilation for it to not drive them insane (the SO2 smell is particularly annoying because it gets stuck in your nose and it's all you smell for at least an hour afterwards even when in fresh air)

I have a suspicion that the mode of action of this toner is quite close to this of hypo alum sepia toner. This toner produces rather cold tones, even a bit purplish in some cases AFAIK.

EDIT: Oops, koraks beat me to it by just a day.

@earlz : Since I was not sure about the correct color balance, I did provide numbers for the image borders. If anything, these frame borders were blue/purple, definitely not yellow. If we bring these frame borders to perfect neutral, assuming that its hue comes from whatever scum deposited on the print, then the rest of the image will turn red/orange.

PS: If there is indeed colloidal sulfur in your print, it will eventually react with the silver. The best way to remove it is by letting this print sit in a tray filled with concentrated solution of Sodium Sulfite, maybe with some Sodium Carbonate to keep its pH high. I have successfully cleaned old fixer bottles with sulfur precipitates that way.

In my experiment I was able to wipe the sludge right off the emulsion without difficulties, when the paper was still wet. It went away without leaving a visible trace.

The precipitate that is formed in the solution was yellowish in my case, suggesting it is indeed elemental sulfur. If it's colloidal or consists of larger particles is not clear to me, but I suspect the latter as the solution was cloudy, which I would not expect with colloidal particles (but I'm not sure about this).