Enlarged salt print process

[Anthony Zingre]

I'm afraid I don't know enough of the science to be of much help here. I didn't do much research, just read somewhere that erythrosin adds to the green sensitivity of emulsions and figured I would try it with salted paper. Jonathan Hilty might be of more help than I can be. He's been working on making autochromes and has created a panchromatic emulsion for them. He helped me a bit with my explorations, I believe he goes by ThePhotoChemist on this forum

Thanks, Ethan! Tonight, when I get home, I'll clear this thought process up a tad and get on with it. Like you, the experiment is the real world for me as well.

 

[Anthony Zingre]

Yes, inherently so. To the best of my knowledge silver salts inherently remain UV-sensitive even if you broaden this spectral sensitivity into the longer wavelengths. In color film this is dealt with using filter layers between the emulsions.



Not too worried about that; silver negatives can take a lot of abuse, it seems.
Have you seen this: https://www.photrio.com/forum/threads/diy-31-megapixel-enlarger.197305
The type of LCD's used in those are primarily intended for (intense) UV exposure. Might be interesting in combination with alt. process printing.



Let's see if we can summon @ThePhotoChemist by alerting him to this thread

Thank you, sir. When I get home tonight I'm posting an experiment in digital but I think... well, you'll see. Back to work.

 

[Anthony Zingre]

Thank you, sir. When I get home tonight I'm posting an experiment in digital but I think... well, you'll see. Back to work.

Ok, home with time to think. My concern and an acquaintance and apparently a few here on this thread was that adding any dye that could cause silver bromide to become sensitive to a specific wavelength is that it would only be sensitive to that wavelength and roughly there abouts. Spreading out the sensitivity might take the emulsion out of the UVA range entirely.
If, as you suggest, the paper remains sensitive to the UVA spectrum, it would seem to me that the light being used for exposure would need some level of compensation for exposure in the invisible range through the visible ranges. If it normally takes time x to see an image print out in the UVA, it would most certainly be a shorter period to expose, all things being equal, visible ranges. Perhaps the mottled look on person describes isn't the paper being insensitive to UVA but a reciprocity error of the emulsion.
Since everyone is talking about LED's being the light source of choice, would some sort of light attenuation between the visible and invisible be possible with a controller to the light head? You know, less intensity here, more time there kind of approach? If I had a LED head to try programing this... I would, and then guage a rough idea from there, mathematically introducing time and intensity across the wavelenths.

 

[koraks]

If it normally takes time x to see an image print out in the UVA, it would most certainly be a shorter period to expose, all things being equal, visible ranges.

Not necessarily; there are a lot of factors possibly spoiling the broth here: the nature of the light source, side-effects of sensitization (this tends to come at the loss of quantum efficiency IIRC) and also the inherent energy of light, which skews by definition towards shorter wavelengths and makes longer wavelengths inherently less powerful.

would some sort of light attenuation between the visible and invisible be possible with a controller to the light head?

If you were to use an array of different LEDs for the visible and invisible wavelengths, you could inch into that direction, but given how an enlarger works, you can't really tailor the wavelength to very specific places. The best you could do is highlight fairly large areas/blobs with specific LEDs, given that they are individually addressable. A lot will depend on the optical design of the enlarger.
With a single high-power COB LED etc. there's virtually no wavelength tailoring possible. Those are monochromatic, and the only wavelength shift you can do is run them close to (or over) their designed power rating, which will shift the wavelength a bit (and run the risk of burning out the LED).

All considered, there seem to be a lot of implicit assumptions underlying the exploration you wrote down above, and I'm not quite sure how accurate they will turn out to be.

The main question, however, is "why"? Can you explain what you're trying to achieve by sensitizing a silver chloride emulsion to a broader spectrum? How is it going to help? If it's about making salt prints compatible with visible light enlargers - wouldn't be a regular enlarging paper be a more obvious choice?

 

[Anthony Zingre]

Not necessarily; there are a lot of factors possibly spoiling the broth here: the nature of the light source, side-effects of sensitization (this tends to come at the loss of quantum efficiency IIRC) and also the inherent energy of light, which skews by definition towards shorter wavelengths and makes longer wavelengths inherently less powerful.



If you were to use an array of different LEDs for the visible and invisible wavelengths, you could inch into that direction, but given how an enlarger works, you can't really tailor the wavelength to very specific places. The best you could do is highlight fairly large areas/blobs with specific LEDs, given that they are individually addressable. A lot will depend on the optical design of the enlarger.
With a single high-power COB LED etc. there's virtually no wavelength tailoring possible. Those are monochromatic, and the only wavelength shift you can do is run them close to (or over) their designed power rating, which will shift the wavelength a bit (and run the risk of burning out the LED).

All considered, there seem to be a lot of implicit assumptions underlying the exploration you wrote down above, and I'm not quite sure how accurate they will turn out to be.

The main question, however, is "why"? Can you explain what you're trying to achieve by sensitizing a silver chloride emulsion to a broader spectrum? How is it going to help? If it's about making salt prints compatible with visible light enlargers - wouldn't be a regular enlarging paper be a more obvious choice?

Hello, Koraks. Thanks for the insight into this. To answer the why part of this involvement with actinic processes, yes, the obvious answer is just work with emulsions or papers designed for enlargement. I suppose they will be here for the foreseeable future. Right? Tbh, and because I've been working with iron salts, toning contact prints on papers unavailable on the commercial market with emulsions applied ( iron or silver ) has always driven me outside. I just assumed, incorrectly, that it wasn't possible to enlarge negatives for an actinic print process, especially on papers I personally like.
There really isn't anything quite like a split toned cyanotype, especially when it's reproduced more than once and not just some happy accident. The thought of carrying the show indoors and under an enlarger, admittedly, excites me, and working with salted paper on the silver side, especially on papers I like, really floats my boat. So, this is a new adventure, one I'm trying to get through the technical aspects of because, as you may have guessed, I know dick all about these light sources we're talking about here, but... thanks to you guys, I'm learning.

 

[koraks]

Yeah, that makes sense and I share your enthusiasm for alternative printing processes

The question remains: why the interest in expanding the spectral sensitivity of a salted paper (silver chloride) emulsion? I can sort of see a benefit if one wants to use e.g. blue instead of UV LEDs - is that the direction you'd be heading into?

 

[nmp]

Yeah, that makes sense and I share your enthusiasm for alternative printing processes

The question remains: why the interest in expanding the spectral sensitivity of a salted paper (silver chloride) emulsion? I can sort of see a benefit if one wants to use e.g. blue instead of UV LEDs - is that the direction you'd be heading into?

Could you not convert a traditional silver gelatin paper to a POP salt by coating some silver nitrate to it and exposing in the conventional enlarger?

:Niranjan.

 

[koraks]

Could you not convert a traditional silver gelatin paper to a POP salt by coating some silver nitrate to it and exposing in the conventional enlarger?

Not in the sense that the silver nitrate will do anything useful with the existing silver gelatin emulsion present on the paper. The silver halide already present is stoichiometrically balanced, so there's nothing for the additional silver nitrate to form a silver halide with.

You could probably coat a silver chloride emulsion on top of a silver gelatin emulsion. However, the silver bromide in the silver gelatin emulsion won't have much of a function and would ideally be fixed out beforehand, and there will be challenges getting the silver chloride to adhere (and evenly, at that) to an existing and hardened gelatin emulsion.

Which is really a long way of saying "I don't think it's a very sensible route to take"

 

[Anthony Zingre]

Yeah, that makes sense and I share your enthusiasm for alternative printing processes

The question remains: why the interest in expanding the spectral sensitivity of a salted paper (silver chloride) emulsion? I can sort of see a benefit if one wants to use e.g. blue instead of UV LEDs - is that the direction you'd

Yeah, that makes sense and I share your enthusiasm for alternative printing processes

The question remains: why the interest in expanding the spectral sensitivity of a salted paper (silver chloride) emulsion? I can sort of see a benefit if one wants to use e.g. blue instead of UV LEDs - is that the direction you'd be heading into?

Good morning. Oh, you were asking the technical "why". Ok. I gotta get to work but given what Ethan experienced, does broadening the spectral response, i.e. more blue light sensitivity, by adding an analine dye like he's done increase the sensitivity of the emulsion only and decrease the amount of exposure time under the enlarger as a POP paper, or does it completely change the nature and is exposing the paper to ultraviolet unnecessary?

 

[nmp]

Not in the sense that the silver nitrate will do anything useful with the existing silver gelatin emulsion present on the paper. The silver halide already present is stoichiometrically balanced, so there's nothing for the additional silver nitrate to form a silver halide with.

New silver nitrate wouldn't be for making new silver halide but provide the excess silver nitrate in the paper which will create the environment conducive for print-out by in-situ physical development. That is the mechanism behind salt print. I think one of the earliest method of Talbot was to coat silver nitrate first, then floating over salt which when followed by thorough washing, left the paper with all silver halide. Then just before exposing he would brush on a small quantity of silver nitrate to make it print-out on exposure.

:Niranjan.

 

[koraks]

That would be an interesting approach for sure. Give it a try?

 

[nmp]

That would be an interesting approach for sure. Give it a try?

Not me...don't have paper or an enlarger. Besides I bet this has been done by someone already.

:Niranjan.

 

[Anthony Zingre]

Good morning. Oh, you were asking the technical "why". Ok. I gotta get to work but given what Ethan experienced, does broadening the spectral response, i.e. more blue light sensitivity, by adding an analine dye like he's done increase the sensitivity of the emulsion only and decrease the amount of exposure time under the enlarger as a POP paper, or does it completely change the nature and is exposing the paper to ultraviolet unnecessary?

Here's the deal. I may have misunderstood what was being said here. I assumed some level of UVA was still necessary even if the sensitivity was shifted to the blue. Since I am more interested in cyanotype, and finding a UVA bulb at 365nm capable of exposing a print in a reasonable amount of time possible, I figured the money I was about to spend was just the way life rolls. I found a Nichia 365nm LED mounted in a E27 base that has an enormous amount of radiative flux, hovering around 8500 uW/cm2 @ 10 inches. That'll blast your eyeballs out even if it's just UVA. Put your yellow glasses on, right? But, with power, there is cost. $360 per bulb. Ouch. So reading about Ethan's work put me on the crazy train trying to find answers for light sources and what light I'm actually looking for.

 

[nmp]

Here's the deal. I may have misunderstood what was being said here. I assumed some level of UVA was still necessary even if the sensitivity was shifted to the blue. Since I am more interested in cyanotype, and finding a UVA bulb at 365nm capable of exposing a print in a reasonable amount of time possible, I figured the money I was about to spend was just the way life rolls. I found a Nichia 365nm LED mounted in a E27 base that has an enormous amount of radiative flux, hovering around 8500 uW/cm2 @ 10 inches. That'll blast your eyeballs out even if it's just UVA. Put your yellow glasses on, right? But, with power, there is cost. $360 per bulb. Ouch. So reading about Ethan's work put me on the crazy train trying to find answers for light sources and what light I'm actually looking for.

OP here using the conventional enlarger with visible light source and adapting the salt print chemistry to make it sensitive in the VIBG area. If you have a UV source, you don't need any extra sensitization.

:Niranjan.

 

[Anthony Zingre]

OP here using the conventional enlarger with visible light source and adapting the salt print chemistry to make it sensitive in the VIBG area. If you have a UV source, you don't need any extra sensitization.

:Niranjan.

Yes, that's understood. The point of sensitization then is to eliminate the need for UV light entirely, correct?

 

[nmp]

Yes, that's understood. The point of sensitization then is to eliminate the need for UV light entirely, correct?

Right. You don't need a $360 bulb either. There are many cheaper options, like LED arrays you can buy much lower prices and fashion a box to house them. Bunch of threads on that subject here if you do a search.

:Niranjan.

 

[NedL]

New silver nitrate wouldn't be for making new silver halide but provide the excess silver nitrate in the paper which will create the environment conducive for print-out by in-situ physical development. That is the mechanism behind salt print. I think one of the earliest method of Talbot was to coat silver nitrate first, then floating over salt which when followed by thorough washing, left the paper with all silver halide. Then just before exposing he would brush on a small quantity of silver nitrate to make it print-out on exposure.

:Niranjan.

I think this is right. The excess silver will form new halides as chloride ( or bromide ) is freed by the reduction of silver. But as Liam Lawless noted in his article, it seems like there is probably more going on than that in the "in-situ physical development"! ( https://unblinkingeye.com/Articles/POP/pop.html ). I guess the resulting POP could probably be exposed under a visible-light enlarger, but it's not obvious! Normal darkroom DOP has various tweaks to affect contrast and variable contrast and I'm not sure if these would apply to the POP made this way or not. The few times I played with painting 1 or 2% AgNO3 onto normal printing paper, I exposed under a large negative in the sun, so... no idea!

 

[Anthony Zingre]

Right. You don't need a $360 bulb either. There are many cheaper options, like LED arrays you can buy much lower prices and fashion a box to house them. Bunch of threads on that subject here if you do a search.

:Niranjan.

Thank you, Niranjan. That clears up the confusion on Ethan's original post.
Tony

 

[koraks]

The excess silver will form new halides as chloride ( or bromide ) is freed by the reduction of silver.

For that to happen, the halide would have to be pretty mobile. I wonder how mobile it really is if it's in a colloid matrix. Perhaps if the emulsion is wet, but when dry, I wouldn't expect to see Br- ions wandering around a lot.

Moreover, there's not a whole lot of conversion happening during a typical exposure anyway, right? It's just tiny bits of individual grains - it takes quite some flux to get any printing out, and you'd have to have a decent amount of printing out to begin with for additional silver nitrate to play a significant role, I'd expect.

I'm afraid I'm not quite bored enough (yet) to try it out...

 

[nmp]

For that to happen, the halide would have to be pretty mobile. I wonder how mobile it really is if it's in a colloid matrix. Perhaps if the emulsion is wet, but when dry, I wouldn't expect to see Br- ions wandering around a lot.

More or less the same when you use a sizing salt in a normal salt print, no? The idea is when a photon reduces silver chloride to silver and chloride, the latter combines readily with the nearby silver nitrate to form new silver chloride which then is available for further photo-reduction. A chain reaction ensues and the density is built up at the same spatial location - increasing the photo-efficiency. There is no such entity to take up the excess halide ions to make new halide in the normal DOP paper, hence the very slow conversion - with long expoures you get a lumen print.... But then one dose not need a lot of conversion since one is going to amplify the small silver formation into the final image using a developer.

:Niranjan.

 

[koraks]

More or less the same when you use a sizing salt in a normal salt print, no?

I'm not sure - when I make salt prints, I coat the salt (coat, float, embed in sizing etc.), then coat on silver nitrate. Insoluble silver chloride is formed as the silver nitrate is added. There may be an excess of silver nitrate, but I don't see how it would play a significant role during exposure. In fact, the first step in processing seems to be aimed at washing away that silver, which in the first wash bath combines with chloride that is released from the paper fiber mesh as it is wetted.

Not saying you're wrong - you probably know better than me, but I don't see how the mechanism is illustrated in a regular salt print process. To the best of my knowledge, it doesn't work that way.

There is no such entity to take up the excess halide ions to make new halide in the normal DOP paper, hence the very slow conversion - with long expoures you get a lumen print...

You get a decent lumen print with similar exposures (to UV!) as a salt print, at least insofar as I've played around with lumen prints (which admittedly isn't that much).

 

[nmp]

I'm not sure - when I make salt prints, I coat the salt (coat, float, embed in sizing etc.), then coat on silver nitrate. Insoluble silver chloride is formed as the silver nitrate is added. There may be an excess of silver nitrate, but I don't see how it would play a significant role during exposure. In fact, the first step in processing seems to be aimed at washing away that silver, which in the first wash bath combines with chloride that is released from the paper fiber mesh as it is wetted.

Not saying you're wrong - you probably know better than me, but I don't see how the mechanism is illustrated in a regular salt print process. To the best of my knowledge, it doesn't work that way.

OK, do an experiment. What I described above by coating the silver first and then dip it in a strong salt solution, then wash so no salt remains in the paper. Dry. Now cut in two pieces - one you brush some silver nitrate again, the other none. Then expose them together.

:Niranjan.

Addendum: I thought I had a deja vu, but turns out we had this discussion long time back: https://www.photrio.com/forum/threads/sciencey-questions-on-pop.141899/#post-1853463

 

[nmp]

Here is what Liam Lawless has to say in his article:
____________________________________________________________________________________

Emulsions for printing-out normally utilise different combinations of silver salts to those intended for development, but the most important difference between the two types is that printing-out emulsions contain an excess of silver nitrate over whatever salts are used, whereas development emulsions normally have an excess of salt over silver. When the solution of a salt such as sodium chloride is combined with silver nitrate solution, silver chloride is formed as a white precipitate, and silver is said to be in excess if there is some silver nitrate left after all of the sodium chloride has been changed into silver chloride, while salt in excess means that some salt remains after all of the silver nitrate has been used up by the reaction.

Sufficient exposure to light (or ultraviolet radiation in this case) liberates the halogen (chlorine, bromine or iodine) from a silver halide crystal to leave just a grain of silver behind, but emulsions without an excess of silver nitrate show little darkening. An explanation that has been put forward for the print-out effect with excess silver (Hermann Vogel, cited by Reilly) is that with an excess of silver, the escaping chlorine (for example) reunites with free silver nitrate to form fresh silver chloride, which in turn forms another grain of silver. With a large excess of silver (and continued exposure!), this “recycling” may take place many times.
____________________________________________________________________________________

Printing Out Paper

:Niranjan.

 

[NedL]

....There may be an excess of silver nitrate, but I don't see how it would play a significant role during exposure....

Definitely there's an excess! You won't get a very good printout if there isn't.. there's a particular "bluish-grey" weak color that happens when pure silver chloride is exposed without enough excess silver.

This is a salt print "problem" that can happen when there is too much salt. For example, if the sizing is thick and retains a lot of salt from floating and not enough sensitizer is brushed on... this is the reason it was traditional to float starch-sized papers on the sensitizer rather than brush it on ( or why Ellie Young had to push a big puddle of sensitizer across her starch-sized prints, and drain off the excess! ), and why some people resort to double coating the sensitizer.... the starch sizing is thick and absorb lots of salt.

But I still don't know if normal DOP w/ silver nitrate brushed on would be sensitive enough to enlarger light to make a good printout