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.
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
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.
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.
would some sort of light attenuation between the visible and invisible be possible with a controller to the light head?
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?
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?
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?
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.
That would be an interesting approach for sure. Give it a try?
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.
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?
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.
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.
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.
More or less the same when you use a sizing salt in a normal salt print, no?
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...
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 may be an excess of silver nitrate, but I don't see how it would play a significant role during exposure....
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