Removing Silver

peeniwali · Dec 14, 2010

Hello all,

I have a project where I am looking to remove all of the metallic silver. Basically I am trying to strip it bare so there is no image at all except where I mask it off.

I was thinking that Farmers reducer or potassium ferricyanide + fixer might do that. I am open to thoughts on this and would love some feedback. Although I would prefer to do this in a single bath I could do it with 2 and that would be just fine.

If I do use potassium ferricyanide can I add that directly to the fixer or do I have to keep the 2 chemicals separate? For some reason I am thinking Farmers reducer is a mix of the two but I am not sure.

Cheers,

Peeniwali

holmburgers · Dec 14, 2010

Farmer's reducer is hypo and K-ferricyanide, and that should work. A potassium-dichromate bleach or potassium-permanganate bleach should work as wel, as per reveral processes.

Mike Wilde · Dec 14, 2010

Film or paper? Ammonia will strip the gelatin layer off pretty quick in my experience. I use this technique occasionally to take dud test prints on papers that I otherwise like the texture of. I then re-coat them for cyanotype prints.

peeniwali · Dec 14, 2010

Mike,

Its on nylon fabric, no gelatin, just silver.

-Peeniwali

Mike Wilde · Dec 15, 2010

Look up tray cleaner formulae- they are usally a mix of an oxidizer and a strong acid of one sort or other, as discussed in this thread. If we are trying to take silver (stains?) off of fabric the acid may atack the nylon first!

Ian Grant · Dec 15, 2010

Iodine in Potassium Iodide solution is the best clean working silver bleach. It's the only one that leaves no trace stains.

Ian

Gerald C Koch · Dec 15, 2010

A mixture of potassium ferricyanide and hypo is unstable. They must be mixed just before use.

CBG · Dec 15, 2010

Ian Grant said:
Iodine in Potassium Iodide solution is the best clean working silver bleach. It's the only one that leaves no trace stains.

Ian

I have a few references to formulae for iodide bleaches. One, the simplest, being:

Pot Iodide 15% solution
Iodine 5% solution

This is diluted 1 to 64 for use.

Would this be what you are referring to? And is it a rehalogenating bleach?

Ian Grant · Dec 15, 2010

That's about right. I use teh Iford formula.

No it's not rehalogenating because of the Iodine, Used too strong it can leave a stain in Gelatin, I found after fixing this goes completely with a quick dip in old dev.

Ian

peeniwali · Dec 15, 2010

All good comments and really appreciated. I need to see what is compatible with the nylon substrate I am using and get going on some test strips.

-Peeniwali

holmburgers · Dec 15, 2010

Care to share exactly what it is you're doing? Inquiring minds want to know!

peeniwali · Dec 15, 2010

Yeah i knew this was coming. Still have no snappy response so I might as well just come out with it. I am removing silver from a coated fabric while masking off the parts I want to keep. I wanted to do it in my darkroom so the extra chemicals could find a useful afterlife in my darkroom.

dehk · Dec 15, 2010

Simple household bleach will do it. It'll take the emulsion off.

Murray Kelly · Dec 17, 2010

50g of copper sulfate and 50g of common salt per litre will strip it off and not ruin the nylon. If there is a lot to do it's easy to make stronger, for convenience.
It rehalogenates in 5 mins or so but I forgot a strip recently for an hour and it was down to clear base.
Otherwise rehalogenate and dissolve the silver salts off with hypo. Still pretty easy on the nylon.
Murray

peeniwali · Dec 17, 2010

copper sulfate and table salt strips metallic silver? Really? If so, thats pretty nice.

Murray Kelly · Dec 18, 2010

The black on B&W negatives is metallic silver. Very fine filaments, but metallic silver none the less.

peeniwali · Dec 18, 2010

i will see if I can order up some copper sulfate and give it a whirl, thanks Murray.

-Peeniwali

Murray Kelly · Dec 18, 2010

Go to the garden section of the local hardware store. Comes in half kilo or 1 pound packs and may be labeled 'bluestone'.

mattmoy_2000 · Dec 18, 2010

I've seen prints partially destroyed (for artistic effect) using copper sulphate bleaching.
If you're interested in the opposite of how this works, you can take tarnished silver, and put it in a bowl of table-salty water, touching a (large) piece of aluminium foil. The silver goes shiny again, because the oxide transfers to the more reactive aluminium.
I suspect that the CuSO4 bleach works by a similar mechanism, whereby the Cu2+ is reduced to Cu or Cu+, and the Ag is oxidised to a Ag+ ion, forming AgCl (or Ag2SO4?) which presumably can then be dissolved in fixer.

Removing Silver

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