[Anya]

Hi all,

I'm relatively new to chemistry (I'm studying on my own), but I'm an analog photographer and keen to experiment with alternate processes and looking to expand my understanding of how the photographic process works beyond simply following a stock recipe.

A few months ago I got to wondering if it would be possible to create a photographic emulsion that substituted copper nitrate for the usual silver nitrate. I've taken a recipe from the web for a basic silver formula and determined the chemical quantities in moles so I could find the appropriate starting point with the copper nitrate.

I was wondering if anyone might have some insights on what I'm attempting. Could this work? or is it totally absurd? My reasoning is that copper is in the same column of the PT, so it might function similarly. Anything I should be taking into account besides the molar ratios?

Also, I just looked up copper nitrate for the chemical formula and found there's "I" and "II" kinds. Copper nitrate(I) seems most analogous to silver nitrate, but would copper nitrate(II) have a chance of working if that's all I can find?

I know it's a lot of questions for a newbie, but any insights would be most helpful.

Thanks in advance. Now back to studying...

~~Anya

[Borek]

IMHO it won't work. Photosensitivity of silver halides is in a way special, and not present in copper halides.

The only application of copper in photographic techniques that I am aware of is to increase the negative density.

[Corribus]

I was wondering if anyone might have some insights on what I'm attempting. Could this work? or is it totally absurd? My reasoning is that copper is in the same column of the PT, so it might function similarly. Anything I should be taking into account besides the molar ratios?

If the sentence I bolded were true, people would wear copper jewelry instead of silver and gold, no?
True, elements in the same group do share some common properties, but that does not mean you can swap them indiscriminately. 

Silver nitrate is used as a precursor to silver chloride generation.  Silver chloride is insoluble and light sensitive: in crystalline form it is easily reduced to form silver metal, which is used to form a photographic image.

Here are three reasons why you probably can't substitute copper for silver.

(1) Silver chloride is a lot less soluble (in water) than copper chloride.  About one thousand times less soluble, in fact. (K_sp for AgCl  Ag⁺ + Cl^- = 1.77 x 10^-10; for the analogous Copper(I) chloride, K_sp = 1.72 x 10^-7 (at 25 °C).  Because Copper(I) chloride is more soluble, you won't form microcrystalline precipitates in your gelatine matrix, so you will have much less photoreduction to copper to make your image.

(2) Silver ions are going to be more easily photoreduced than copper ions are.  The reduction potential for Ag⁺ + e^-  Ag⁰ is 0.7996 V.  For Cu⁺ + e^-  Cu⁰ it is 0.521 V.  (25 °C, STP).  That's a pretty significant difference.  You could probably put some test numbers into the Nernst equation to find out relative rates of photoreduction if you wanted to, but the important thing here is that image generation (even pre-development latent image) requires formation of metal specks from photoreduction of metal ions.  If you can't form the metal specks easily, you won't get a good image.

(3) Copper metal is more easily oxidized (reverse of 2) than silver.  A copper-based image will be far less stable in air than a silver based image.

Plus there's just the fact that copper is a lot cheaper than silver.  If it was a good replacement, that's what people would probably be using.

EDIT: By the way, it was a nice question.  I like it when people think about the chemistry behind what they do in their daily life.  Keep it up!!

[Borek]

to increase the negative density.

Just in case: optical density, not density in g/mL

[Anya]

Thanks for the replies. I would have followed up earlier but sociology (my major) and other obligations got in the way.

Corribus, you make some interesting points, which I hadn't considered (probably due to my newbieness in chemistry). #3 I think ultimately is a matter of esthetics, especially as darkroom/chemical photography is now largely relegated to artists rather than professional/commercial photographers. It would make for an interesting print if the print would ultimately patina like raw copper, or some similar transformation.

#1 could most likely be overcome by using a copper bromide based emulsion, which, at 6.27 x 10^-9, approaches that of silver chloride. Photographic papers have traditionally been made in both chloride and bromide forms, so starting with a bromide based formula would give the best chance of a workable outcome based on this factor.

#2 is the point I'm still having trouble wrapping my head around, and maybe I just need to study more general chemistry to get there. The reduction potential does seem like a significant difference, but could that be reasonable overcome with greater/more intense light exposure, either as a longer exposure time under an enlarger or, as is common with other historical processes like platinum and palladium, exposure under direct sunlight/UV light?

I did stumble upon a patent describing a photographic process using cuprous nitrate, though I haven't been able to fully digest it yet. I do think it involves using silver nitrate and copper to produce the copper(I) nitrate, and it mentioned that the silver is recovered in the process.

I am, however, going to give it a shot. I've ordered some copper nitrate and hope to play next week. All I've got to lose is a small monetary investment, and whether the experiment(s) work or not, it will be knowledge gained. If anything develops (pun sort of intended), I'll report. I'll consider success to be any sign of photosensitivity with some selectivity to form even a relatively thin image.

BTW, as far as copper jewelry goes, copper is, in fact, my favorite metal for jewelry, second only perhaps to rose gold. I just like the warm orange color better than yellow gold. Maybe that's what got me started on this idea...

Meanwhile, any other thoughts or considerations would be appreciated.

~~Anya

[Corribus]

Well a good experiment is always superior to good theorizing.  Let us know how it turns out!

[Mujuni Chris]

then what is the melting of tristhioureacopper(i) sulphate