Removing Silver

[peeniwali]

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]

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]

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]

Mike,

Its on nylon fabric, no gelatin, just silver.

-Peeniwali

 

[Mike Wilde]

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]

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]

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

 

[CBG]

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]

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]

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]

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

 

[peeniwali]

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]

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

 

[Murray Kelly]

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]

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

 

[Murray Kelly]

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

 

[peeniwali]

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

-Peeniwali

 

[Murray Kelly]

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]

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.