Metallic stains on sepia toned prints
Lately, I have tried to sepia tone a number of liquid emulsion prints (Rollie Black Magic VC). The toner I used is Amaloco T-10 Sepiton, a dutch product of which I am not to sure others know about or if it's sold outside the Netherlands. Unfortunately, the exact contents of this toner is not mentioned on the package. However, it is a two bath system, and it does mention ferricyanide and sodiumhydroxide for the first and second bath respectively. Based on some research I've done on the internet, I know suspect, or almost know for sure, that it is a thiourea based sepia toner, since the other two types of sepia toner either are not odourless and single bath (sodium sulphide based sepia toners), or can not be combined with any alkaline solution like the sodium hydroxide in the second bath, since that would destroy it (metal ferricyanide toners - copper based for sepia). So it's most likely a thiourea based toner.
Anyway, the problem I've seen turning up is that metalic / silvery stains appear in the *most dense/dark parts* of the sepia toned prints, so those parts of the original photo that had the deepest blacks. Actually, although I'm pretty sure I've stayed below the stated capacity of the toner (in terms of square meters), I am suspecting I may simply have exhausted the toning bath (the second sodium hydroxide / thiourea bath). Toning times were already rising, and I may simply not have fully toned all bleached silver. Many of my prints are also very dark, so requiring a lot of the toning bath...
Is this indeed possible??? Or am I talking complete nonsense here? Does untoned, but bleached silver, turn into a visible metalic layer on sepia toned images when the toning bath is exhausted? And if not, does anyone know the real cause of these metalic / silvery stains?
Thanks for any info!
No one?... I guess I have possible answered the question myself, but it would be nice to have some confirmation of someone with more experience in sepia toning...
With "metallic" by the way, I mean that these parts also look very shiny / reflective, compared to the rest of the print which has a matte surface. This is especially apparent when I turn the print around relative to a fixed light source. I see a kind of metallic surface popping up than.
Are you toning in metal trays? I don't know if this is the cuase of your problem, but many toner directions will tell you not to tone in metal trays; at least not in metal trays where the paint is chipped.
I have always used plastic trays for toning.
I have seen this three or four times and always in the same batch of prints but have no idea of its cause. I find that when I see this in the toner, rubbing the effected area will usually remove the problem (use gloves or a cotton-bud etc as thiourea is reportedly carcinogenic, but I don't know to what degree by absorption).
I'm pretty sure neither baths were exhausted so I'm wondering if it is insufficient washing causing a carryover from the fixer or carryover of the bleach to the toner. Both seem unlikely as I'm pretty careful of both, but I don't rule either out completely...
I use plastic trays exclusively.
'Tis a mystery to me...
No, I use plastic trays. The only metal is the stainless steel from the tongs, but these have rubber tips and the metal does not seem to have been corroded in any way by the baths.
I still suspect incomplete toning by the second sodiumhydroxide / thiourea bath, leaving bleached silver in the image. I am thinking of a test by throwing the affected prints back into fresh bleach and toner baths. If it is indeed a layer of metallic silver, I suspect I should be able to bleach and tone it again.
Maybe it would be good to fix toned prints as well using a normal fixing bath?? This should get rid of any left over bleached silver, if I have understood some other stuff I have lately read on the internet (not specific to toning by the way).
Anyone doing this after (sepia) toning???
Thanks Bob for your response, good to know others have had similar issues. I will let you know what my test results are...
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I have experianced similar effects which I too think are the result of toner exhaustion. I now follow Tim Rudman's advice, and refix after any toning that involves a bleaching stage in order to remove any unfixed silver halides left.
Originally Posted by Marco B
Bob mailed me and asked me to chime in. I'm on the road right now shooting for a few more weeks and so rely on WiFi when it is available - or not.
It would be interesting to see these. Copper does this easily but I haven't seen it with Thiourea toners. Thiourea sepia often leaves a white deposit which dissolved in 3% acetic acid or simply some dilute stop bath, but it doesn't look metallic (to my eye).
Fixing after incomplete toning would be wise, but expect some loss of tone - and why tone incompletely? better to control at the bleach stage and tone fully.
Perhaps you can get the toner ingredients from the maker? They might respond, but anyway they should at least have a data sheet (MSDS or hazard substance list etc should be available for users)
Thanks for joining in, and thanks to Bob for contacting you. Considering the number of references to you on APUG, and your book, you seem to be one of major experts here on APUG...
Sorry for the late response by the way, my "online" status of the past week was a bit fudged to say the least, as my computer was down but APUG doesn't automatically log you out...
I've now done some further research, by reading some articles on the internet, and a bit of experimentation.
First of: I've done the test to try to re-tone the image with fresh toner solution. Both the bleach and toning baths failed to have any effect at all at the staining. So "metalic" silver is almost out of the question.
Well, reading some more stuff about the workings of (sepia) toners, silly me to even think this was reduced silver. For the silver cation to be reduced to metalic silver, would require at least some reducer / electron donor. Bleach has just the opposite effect, oxidizing the Ag to Ag+ in the form of most likely AgBr, silverbromide, if the bleaching bath has potassiumbromide in it as well (as with most of the sepia toners according to what i've read...). Else, in the absence of bromide, a silverferrocyanide deposit would be formed.
The toning bath subsequently doesn't do a reduction either on the silver, it merely bounds the Ag+ cation to sulphur, in the process destroying the intermediate silverbromide and resulting in the stable Ag2S component, which is the end result of the toning.
So, what next?
Reading through all the stuff, and again having a close look at my stained pictures, I now have a crazy idea I would like your opinion about. To recap my observations (and see the screenshot I now included!):
- Staining is almost exclusively limited to the highest density / black areas of the original print
- Staining starts when the bath is almost exhausted, with long toning times in the second toning bath
- I have now also been able to confirm Bob's observation: Initially, I thought the stains appeared *after* having left the toning bath (thiourea / natriumhydroxide), but this isn't true. As Bob observed, I've now seen in a used toning bath the *temporary* formation of these stains, that disappeared with some more agitation of the bath.
- As another new observation, the stains do not only appear more reflective / metalic, but might be "bleu-ish" as well.
So, here's my crazy idea:
Could the stains actually be "prussian blue", ferriferrocyanide deposit, as formed in blue toners and the cyanotype process?
I know it sounds crazy, because metal-ferrocyanide compounds are supposed to be highly unstable in alkaline environments. However, just looking at the chemical components available in the solutions, there is not much choice, just potassium, sodium, silver and iron are available as the cations to form any kind of stable deposit with the ferrocyanide anion. Ferriferrocyanide deposit is bleu, and might explain the bleu-ish tint of the staining. In addition, it would also explain why some more agitation or "rubbing" as Bob suggested, removes the stains, as this probably helps the weakened alkaline solution to break down the stains...
Maybe that in exhausted toning bath, and especially in the high density silverbromide areas of the bleached prints, a specific "micro environment" can exist that IS favorable of the formation of prussian blue, despite it's vulnerability to alkaline environments. Of course, with the toning bath almost exhausted, the amount of harmful hydroxide anions is likely to be a lot lower...
Just leaves the big question, why dumping the stained print back in the alkaline toning bath, doesn't remove the stains either. Well, reading all the stuff, I know also now that the chemistry of all these reactions, and the products they form, can actually be quite involved, and some forms of prussian blue are more stable than others, as we've been thoroughly discussing in this thread:
The only other option I see, is some deposit of selenium, caused by contamination. Admittedly, I still need to buy some extra trays, but I've only toned once with selenium, and all the initially toned images, using the fresh toner, came out OK before the staining started (and the selenium toning was NOT in between these sessions, but well before that). Seems highly unlikely and besides, why a "reversible" staining than? and only some of darkest parts affected?... and it would need a "major" contamination of the trays causing so much staining I guesse... I rinse them well after usage...
It all doesn't make much sense
Well, interesting to hear what all of you think!...
Attachement showing stains:
Prussian Blue is not a likely cause for this Marco and in any case, in the photographic media, it is notoriously unstable in the presence of alkali. NaOH is a strong alkali and quickly sees off the colour of iron blue in a silver print.
Similarly, Selenium is not likely to be involved in this IMO, for the good reasons you have mentioned and I think both of these are 'red herrings'.
From what you said in your 1st post you are not sure of the ingredients of this toner. From your description, it seems likely that it is a thiourea toner, but I have used thiourea toners regularly and frequently for many years and don't recall getting blue metallic shadows in any of them - unless combined with another agent such as a metal ferrocyanide, so it would definitely be worth contacting the manufacturers, explaining your problem and asking if they can help with an explanation, or at least provide you with an ingredient list or MSDS data sheet. This just might shed some light on your problem.
this may possibly not be what you want to hear, I know, but it's usually best to start with first principles and basic data ;-)
Yes, I think I will need to do that, and contact the manufacturer.
One thing intrigues me though. You disqualify of the possibility of Prussian blue being formed, yet you do point to the possibility of a metal ferrocyanide (which Prussian blue is also). However, according to this excellent article by Wilco Oelen:
*all* metal ferrocyanide compounds are supposed to be instable in alkaline environments. The article is about a vanadium toner, but explains some of the metal ferrocyanide toning chemistry as well. For the alkali susceptibility, see the section "Chemistry of extensions of the toner".
So in what direction are you possibly thinking
Thanks for your response by the way...