FOMA liquid emulsion on silver

Hello!
I'm trying to develope photos onto my handmade silver jewelry using FOMA emulsion. It worked quite well with polyurethane clear coating. I don't like using it thou so I have tried photographic gelatine coating with albumen fixer instead.

It looks good until I drop the jewelry into the illford rapid fixer bath. Of some reason the silver underneath the gelatine turns black on some areas, like silver does when I gets in contact with sulphur. The untreated silver is not affected.

Why is this happening? Can it be prevented?

The main reason that I don't want to use polyurethane is that I have heard that all oil based pu will yellow over time(even thou it's written on the product it won't...). Anybody has any input there? Are we talking 1, 10 or 50 years? I will cover it with uv resistant acrylic coat so uv should not be a problem.

Has anybody tried using Krylon acrylic clear coating as subbing? I don't think it's water based.

Welcome to Photrio @Jonas242 !
Frankly, if the PU works well, I'd just use that. A thin layer, even if it yellows a tiny bit, won't have much of an effect on the image tone. It may shift to a little warmer hue over the years, but I doubt anyone would really notice and whether it's really a problem. Generally, yellowing processes like these are moderated by factors like temperature and exposure to UV light. I'm sorry, I couldn't give an estimate whether any yellowing will really take place, how long it'll take and how much yellowing there will be at the end.

My concern with other coatings is that the adhesion may not be perfect over the years. Frankly, I think that's much more of a concern than the yellowing. You don't want the subbing layer beneath the silver gelatin image to start peeling off of the underlying metal. It'll look horrible.

I really do like the concept though; nice work!

Thanks for the reply!
Yes I might continue along the pu road. I was just so happy when I found out that gelatine, which is a less toxic produc, could work. I really dislike pu since it's 2 component and u need white wash to diluting and cleaning. Smells terrible and if you want the spray can version you have to use everything at once. I have to do hundreds of pendants to empty a whole can .

I have no id if gelatine will stick to the silver over time but it sticks well and seems quite tough before I spray coat it with acrylic clear coat. But like you said, it would be terrible if it peels off after a year.

Nice to hear that you like the concept! I also like the id of silver creating an image on silver.

Jonas242 said:

The main reason that I don't want to use polyurethane is that I have heard that all oil based pu will yellow over time(even thou it's written on the product it won't...). Anybody has any input there? Are we talking 1, 10 or 50 years? I will cover it with uv resistant acrylic coat so uv should not be a problem.

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You may have difficulty getting an acrylic coat to stick to oil-based polyurethane. You can use a water-based polyurethane, which will never yellow and is perfectly clear, and your acrylic top coat may (or may not) stick to that. You'd need to test.

Water based polyurethane is quite water-resistant once cured. Possibly as water-resistant as oil-based.

Thanks for your reply! Lots of knowledge in here. It would be great if water based pu works but I have tried with Vallejo pu water based varnish and it dissolved during the development process. Do you know any brand that works? Maybe I didn't let it cure long enough? I think I waited 24h.

Varathane Diamond water-based is all I've used. But I haven't put it on silver. Any amount of oil on the silver will make it not stick, is my guess. And I'm not completely sure that it wouldn't immediately start to tarnish the silver. It's something you'd need to test.

No subbing I have tried so far has tarnished the silver by itself. It's some weird effect from combining the albumen gelatine, Foma emulsion and the fixer. I will see if I can find that brand here in Sweden. I'm not 100% sure I cleaned all grease off with ethanol when I used the Vallejo either so I might try it again.

Did you use glossy or satin?

I've only used it as a wood finish. Water doesn't get through it, in that use. I don't know how much of a difference there is between satin and glossy for your purposes.

Don_ih said:

You may have difficulty getting an acrylic coat to stick to oil-based polyurethane.

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I don't think that's a concern; the acrylic would be an alternative to the polyurethane. It wouldn't come on top of it the way I read it.

Jonas242 said:

I have no id if gelatine will stick to the silver over time

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Maybe; it depends a bit on how it's applied. 'Subbing' (a term sometimes used for treating a surface so that gelatin will adhere to it) is a bit of an art. Companies like Fuji and Kodak spent millions to figure it out for the materials they use.
My main concern with the use of gelatin as a subbing layer in your application is that the gelatin adhesion layer will be water-permeable. So your problem with the fixer darkening the underlying silver will remain the same, I expect. Stuff like PU actually seals the surface.

If you want to try an all-gelatin route, I'd start by very thoroughly cleaning the silver, then dip the silver item in a solution of maybe 0.5% w/v gelatin (0.5g dry gelatin to 100ml water), then let it drip out and dry naturally. I'd also recommend hardening this layer; either add a little bit of chrome alum to the gelatin solution immediately before use (discard the solution after you're done with it; it won't keep). Or harden the gelatin subbing layer after it has dried by dipping in a weak solution of acidified potassium alum, chrome alum, formalin, glutaraldehyde or whatever hardening agent you fancy. They all have their pros & cons.

The dipping approach should leave a very, very thin layer of gelatin on the silver item. This layer will act as a surface the gelatin emulsion can then adhere to. Again, I expect your odd interaction with the fixer will remain a problem if you do this.

koraks said:

the acrylic would be an alternative to the polyurethane

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He said

Jonas242 said:

I will cover it with uv resistant acrylic coat so uv should not be a problem.

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It's probably ok if the acrylic clear coat is oil based.

OK, sorry, I missed that.