Using iodide and bromide in salt prints?

So I've seen a number of threads but pretty much nothing concrete on what happens when using iodide nor bromide in salt prints. Specifically no formulas or actual results, just vague descriptions like "it's a bit faster" or "it's closer to neutral tone"... and no real guidance on mixing different salts in this process.

Going on that lack of information, I figure why not do it myself while also figuring out sizing and the best papers I have for this.

My formula for the salt bath is as so:

* 12g photo gelatin
* 200ml distilled water (let it bloom 20m, then heat to melting)
* Top to 800ml with water
* 10g citric acid
* 15g ammonium chloride
* 1g potassium bromide
* 2g potassium iodide
* Top to 1L
* Coat paper using immersion method

I just mixed this formula and coated a few papers, so too late for advice now, but anyone have anything toward this or suggestions?

I plan on sensitizing the paper using a plain (no citric acid) 10% silver nitrate solution and the foam brush method.

To be processed doing:

* Coat paper in salts, hang dry for 1 day (note: I live in low humidity Colorado, but house humidity is average 40%)
* Brush sensitizer onto paper
* Dry using hair dryer on "warm" setting and high fan speed
* Exposure using UV light panel
* First rinse in silver chloride solution (~10% if I were to guess)
* Rinse more using tap water
* Fix using TF-5 fixer (I've noticed no bleaching from this in chloride salt prints)
* Rinse more using tap water
* Dry in print rack

I did a test sensitization last night. Seems to look very slightly higher contrast and very slightly faster than my pure chloride formula. Tones are still extremely warm. dmax is still weak, but I think this is because of a lack of silver nitrate. I'll try remixing my 10% solution to be 20% and see if that helps things. Where I accidentally double coated on the edge of the test paper was signfiicantly improved in terms of dmax... However, I'm completely uncertain what the purpose of these other salts would serve here. Do I need more silver nitrate for them to begin to matter? Or do I need to increase the ratio of bromide/iodide to get any meaningful effect?

On the plus side, the increase in gelatin from 2g to 12g really seemed to improve the finish of the final product (less "powdery" feeling) and made it quite a bit easier to work with.

I did some testing at some point of different salts for salted paper prints. Potassium bromide gave results fairly similar to NaCl, but with less dmax. Iodide didn't work well at all as I recall; very weak image and useless contrast. I didn't try mixing them, but did separate experiments. I didn't test very systematically; just a quick & dirty test. Based on the results I just stuck with NaCl which seems to be the superior option in the end.

I'd suggest also testing the salts separately to get a feeling for how they work on their own, and only then start mixing them. There might be some room for improvement compared to pure NaCl but my feeling is that you'll end up at something like 0.1% iodine and 1-10% bromide as a good mix, but with only marginal better performance than NaCl. This is just speculation though.

I'm also not too sure about the use of ammonium chloride. Introducing ammonium tends to create problems with fogging pretty easily.

koraks said:

I did some testing at some point of different salts for salted paper prints. Potassium bromide gave results fairly similar to NaCl, but with less dmax. Iodide didn't work well at all as I recall; very weak image and useless contrast. I didn't try mixing them, but did separate experiments. I didn't test very systematically; just a quick & dirty test. Based on the results I just stuck with NaCl which seems to be the superior option in the end.

I'd suggest also testing the salts separately to get a feeling for how they work on their own, and only then start mixing them. There might be some room for improvement compared to pure NaCl but my feeling is that you'll end up at something like 0.1% iodine and 1-10% bromide as a good mix, but with only marginal better performance than NaCl. This is just speculation though.

I'm also not too sure about the use of ammonium chloride. Introducing ammonium tends to create problems with fogging pretty easily.

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I mixed my existing silver solution up to 20% and tried a coating with it. Definitely seems to amp up dmax and contrast quite a bit, but still poor speed with my UV source. I have a new panel on order that should be deeper into the UVA spectrum and hopefully will be a bit faster for this. Another question is what would UVC do to a print? I imagine it might be destructive to the paper and ozone production would be another issue, but might be interesting regardless.

Anyway, my salt mix seems to give a more brown tone on dry-down, but still very warm in appearance. Keeping a test strip overnight revealed it had quite a bit of fogging, but I am fine with my current process where I sensitize and dry the print just before exposure, so this isn't too bad of a problem to have. The ammonium salt was used because it's noted to give warmer red tone results and also keeps pH a bit lower.

Here are the results, still need to work on the internegative obviously, but the material shows promise

Wet: https://i.imgur.com/WcSr5AU.jpg
Dry (bottom was still a bit wet) : https://i.imgur.com/FO9yWYa.jpg

I decided to go out on a tangent tonight and tried making salt prints, but developed it out. It's quite the challenge though. I had to dilute my silver nitrate solution WAY down. I likely had about 5ml of 20% solution and added about 100ml of water. This surprisingly still gave an extremely deep dmax when developed. The "emulsion" overall was still almost only sensitive to UV, but unfortunately it had a very poor and foggy dmin. I'm not really understanding where the dmin problem is coming from. It seems like too much silver nitrate will just outright cause fog, but even dilution to the point where dmax was rather weak, I still got a foggy dmin.

If there is some way of solving this, it's a pretty interesting way to make UV contact printing papers, since it's so much easier than coating an actual emulsion and has a unique vintage appearance despite being neutral tone. Maybe it even comes down to my developer choice (ansco 130 1+1 with benzotriazole) and this needs a very gentle development approach. Regardless, it's interesting to know that there is potential there, though I have a feeling there's a reason no one does this. One big issue when doing the DOP route is that there is no expected excess of silver nitrate. So, any uneven coating of the sensitizer will result in uneven density. I'm unsure there's any good way at all to solve this using brushes, but of course using a puddle pusher might work, but I have a feeling there'd be problems there as well with something that needs precision like this. Thinking about it more, maybe it's possible with specialized equipment, like an emulsion waterfall style machine to put down a perfectly precise layer of silver nitrate, but at that point there's a lot of advantages to just making a traditional emulsion.

It might be possible to make an emulsion style salt layer (ie, 20+% gelatin) and then laying down silver nitrate on top as water. With pre-wetting (to flatten it) and post rinsing, I could imagine this might be precise enough since the gelatin layer would moderate and even out any excess of silver nitrate solution, and importantly minor variations in gelatin thickness would not be too important since the design is for silver nitrate to not reach the bottom of the gelatin... but that still puts me yet again at the annoying process of coating an emulsion onto paper, a distinctly not very fun (for me) hobby. The only potential upside to make this worth it is if this can bring some kind of advantage that's not possible with traditional emulsions... but that seems like a rather slim opportunity. Maybe a surfacant or something could also be added to the sensitizer solution to even prevent needed to pre-wet the paper, or the emulsion could be hardened and then dipped in a tray of silver nitrate, if the backside were protected somehow (would require very hard pre-sizing before salt sizing??)

Potential gains compared to traditional emulsions:

* Less precision required in coating, can allow for much thicker emulsions than is traditionally possible (since silver nitrate won't go deeper than fixer and developer could)
* DOP is naturally much faster than POP. In my simple tests it still required UV for any amount of real speed, but exposure was measured in seconds rather than minutes using a simple UV LED panel
* Can be done one sheet at a time
* No risk of the emulsion being too thick, assuming neutral salts are used that won't harm anything if left in the bottom of the emulsion

Big losses compared to the simplicity of salt prints:

* Would require extensive rinsing under safelight
* Would require final drying in darkness
* Likely requires proper emulsion style coating of the salt solution
* Does not give the nice color of salt prints and contrast seems much higher, similar to traditional materials
* Still requires UV exposure

Either way, definitely a fun concept to kick around, and maybe there's some ways to mitigate some of the losses. For instance, maybe excess silver nitrate can simply be rinsed off after exposure and before development. And maybe dunking of paper into a hardened emulsion mixture would be consistent enough to work here. This process is at least mildly blue light sensitive, maybe different salts could increase that like pure bromide, or even the potential of adding an ortho dye into the salt layer.

edit: The best test print I got out of it, 12s exposure to UV panel that typically requires 30+m https://i.imgur.com/865cVyi.png

I once did an attempt with developing salt prints as well. As I recall I used something like a 1+500 dilution of rodinal because I'd only get fog otherwise. The outcome was quite similar to your print. Exposure time was very short as you also noticed. I didn't pursue it further.

koraks said:

I once did an attempt with developing salt prints as well. As I recall I used something like a 1+500 dilution of rodinal because I'd only get fog otherwise. The outcome was quite similar to your print. Exposure time was very short as you also noticed. I didn't pursue it further.

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the weird thing is I don't really understand where the fog is coming from. There is no ripening and minimal digestion so one would think that the grain size should be very small and thus fog levels very low. Maybe it's just not enough salt and too much silver nitrate

I tried a method, it was about a 90% failure. I think I'm done with my attempts heh.

Process I used was something like:

600ml water
20g sodium chloride
60g photo gelatin
1g citric acid
0.5ml photoflo 200 ("finals")
15 drops of glyoxal ("finals")

I had it heated to around 115F in a beaker, then poured it into a room temp tray, target temp for "coating" was 110F. I coated the paper simply by immersing it. This worked better than expected, but drying a double sided paper is uhh... non-trivial. Since gelatin thickness consistency was not at all important here, it ended up working well enough though. Most defects such as bubbles became invisible after it was dried.

Everything afterwards is where things started to go crazy. I tried a few different sensitization methods. Most were something like 2-5ml of 20% silver nitrate per paper with 50-200ml of water. The problem however is that the salt in the gelatin was still water soluble, and there was a lot of salt. So the silver solution upon contact with the paper nearly instantly turned into silver chloride. This action did not happen inside of the emulsion like I was expecting, but rather tended to just float on top of the emulsion. I tried a few different sensitization methods, including foam brush, puddle pusher, and tray immersion. The tray immersion method surprisingly worked the best. It was 4ml of silver nitrate added to 200ml of distilled water, then put into a tray. Immerse paper in it and quickly agitate. Take paper out and dry very carefully. I used a hair dryer for drying just because I didn't want to wait 8+ hours to see if each method worked. The tray immersion one is the only method that actually made a poor, but recognizable image in printing. All tests were exposed to UV light for 1-2m (with a negative), and processed in ansco 130+benzotriazole, citric acid stop, then TF-5 fixer. Most interestingly, if I was extremely careful with the coated paper, I could get an uneven, but very striking "silvered" appearance, resembling that of pencil graphite type drawings, reflective and shifting from a dull grey to shiny bronze. This is basically dichroic fogging since this image could literally be rubbed off of the paper. However, in other non-image making tests, I found that if this was very carefully handled and allowed to dry, the image was quite robust, only rubbing off if wet and otherwise being quite impervious to the rub test. I also tested fixing, which I feared would not work with such a thick emulsion. Actually removing the fixer completely proved extremely difficult, but the image otherwise would not change at all after fixing. In theory, though the gelatin layer is very thick, the image layer is extremely thin and floating on top. One big problem was that the emulsion is extremely fragile, very easy to damage even using cold (~50F) water when rinsing, I still ended up getting some emulsion peelups. The sheer thickness of the emulsion is I assume the cause, though when dry the emulsion seems to not be fragile at all.

I think I'm going back to regular POP salt prints for now, but it is an interesting process to consider kicking around. I considered if I could make the process work, and I think it is very much possible, but requires a whole lot more work than a salt print and for unknown benefit as it's still almost as much work as a traditional emulsion. My best idea is the following:

* Soak paper in citric acid to neutralize
* Do an immersion style coating of salt-gelatin (maybe 600ml / 5g chloride / 20g gelatin / 25 drops glyoxal) to function as the "base salt layer", and dry
* Do an emulsion style coating of unsalted gelatin (unhardened, thickness consistency is important and should be fairly thick) to function as the "image medium", and dry
* The paper from here can be stock piled for a long time, until mold attacks the gelatin or something anyway
* Do a puddle pusher style sensitization using something like 1ml 20% silver nitrate per 25ml water
* Process as DOP, use a pre-rinse of weak salt solution after exposure but before development to remove any remaining silver nitrate

The expected result here is that basically as soon as the silver nitrate touches the gelatin in this case, it kinda just does nothing and seeps through the "image medium" layer. Once it reaches the base salt layer though, that gelatin will be wetted and make its salt easily available for the silver nitrate to react with, forming silver chloride within the upper image medium layer. The risk here though is that the ratio of salt to silver likely requires some precision. Too much silver in comparison and it'll fog like POP paper does when developed. Too little silver and the salt will reach the top layer, leading to the failures that I've already experienced with silver chloride sitting on top of the emulsion. The other risk is how to prevent the image medium from becoming salted during coating.

Either way, too complex for me right now. I'm going to get back to plain simple salt prints, including a test run where I test each of the three salts and a few mixtures to see what happens.

what a complicated way of making salt prints. ...
I just mix the salt into the gelatin, coat the paper, dry it
then coat it with silver nitrate.

jnantz said:

what a complicated way of making salt prints. ...
I just mix the salt into the gelatin, coat the paper, dry it
then coat it with silver nitrate.

Click to expand...

normal salt prints are definitely a lot easier. I'm going back to that and figuring out a reasonable method of making sheet negatives from 35mm negatives

Funny... I just tried a iodide/silver nitrate print this morning. I go an image, but with very low Dmax. I wonder if combing a salt solution with the iodide solution would help... Most likely it will, but at the end of the day I'll probably just go back to the straight 2% salt solution. The only reason I'm doing this is to see if print colour is different than a straight salt solution...

I didn't see this thread originally. Just a couple random thoughts.

Silver iodide is much more difficult to remove with sodium thiosulfate than silver chloride or silver bromide. It has a yellowish color, and it's usually possible to visually determine if fixing is complete. It could easily take 3 or 4 or 5 times as long to remove silver iodide. I don't know about ammonium thiosulfate rapid fixer, but suspect it would be much faster and might not damage a DOP.

I think the idea of making DOP salt prints using drastically reduced silver makes good sense and is probably more manageable than using highly diluted developer.

I'm not sure where the fog was coming from either. This thread made me remember that this is something I want to try!

grainyvision said:

the weird thing is I don't really understand where the fog is coming from. There is no ripening and minimal digestion so one would think that the grain size should be very small and thus fog levels very low. Maybe it's just not enough salt and too much silver nitrate

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The fog is possibly coming from speed drying the silver nitrate with a hair dryer. NO HEAT, If you must use the dryer turn off the heat, but better to use a low speed fan with room temp air.

That is a possibility. I abandoned the hair dryer a while back, due to that reason, but mainly because some of the processes I use employ dichromates...Don't want to breath in airborne dichromate particles! Anyhoo... no dichromates thankfully in Salt printing but it doesn't hurt to give air drying a go. I use a fan set to low...

Rick A said:

The fog is possibly coming from speed drying the silver nitrate with a hair dryer.

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I've never worked with an alt process that responded this way. Fogging always turned out to be due to other factors than blasting with a hairdryer.

What is the possibility of some uv output from the heating coil in the hair dryer causing the fog? (I really have no idea.)

Don_ih said:

What is the possibility of some uv output from the heating coil in the hair dryer causing the fog? (I really have no idea.)

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None. Long wavelength IR, yes. And a tiny bit of short wave IR and visible in the orange and red parts of the spectrum. But that's the other end of the spectrum from UV. The heat from a hairdryer just doesn't fog stuff like salt prints.

Like always, it's probably the paper. A calotype is basically paper with silver iodide. The great problem for making calotypes is finding paper that doesn't fog... and almost every method of making them ends up with paper that doesn't keep very long before fog starts. The only two exceptions to this that I know of ( processes of Pelegry and his student Trutat ) use a tannic acid preservative after meticulous washing to remove every impurity once the silver iodide is formed. I went through a lot of different kinds of paper before I found one that could work... and even then it needed to be used within about 6 or 7 hours of being dry. Heat definitely played a role in how fast the fog starts up.... the paper will keep a little longer if it remains cool and dark. On a warm day, the fog starts sooner.

I had to go back to my old chemistry books for the reason, heating silver nitrate turns it brown. Using a hair dryer can cause hot spots. I've always had in the back of my brain not to heat it.

Rick A said:

I had to go back to my old chemistry books for the reason, heating silver nitrate turns it brown. Using a hair dryer can cause hot spots. I've always had in the back of my brain not to heat it.

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Silver nitrate decomposes when heated:

2 AgNO3(l) → 2 Ag(s) + O2(g) + 2 NO2(g)
Qualitatively, decomposition is negligible below the melting point, but becomes appreciable around 250 °C and fully decomposes at 440 °C.

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I dunno about your hair dryer, but mine sure as heck doesn't come anywhere close to 250C.
I've never seen brown spots appear in silver-nitrate based, sensitized alt. process papers due to hair dryer use, despite my consistent use of a hair dryer for this purpose (maximum heat, close distance). What does happen easily is chemical interactions between already present pollutants in the paper and the silver nitrate (or in-situ formed silver chloride etc.), and these will be accelerated by higher temperatures.

Koraks, agree. There's an old "rule of thumb" that chemical reaction rates double for each 10°C temperature increase. It's not exactly right or always applicable, but in this case unwanted reactions making fog often go faster if it's warmer...