harvesting silver from over-exposed paper - Page 4

Kirk Keyes · 05-09-2008, 03:32 PM

Quote:

Originally Posted by gainer

FYI, ferricyanide is not cyanide.

Well, it's 6 cyanide ions complexed with one ferric iron ion.

The complex is pretty strong, and you must use contitions that you will most likely not encounter in a darkroom (i.e. hot temps and strong acid). So it's quite save for darkroom use.

Simple cyanides like sodium or potassium cyanide will release cyanide gas with only mild acidic conditions - the cyanide is not complexed in simple cyanides.

knoxissimpler · 05-10-2008, 09:47 AM

wait, is ferricyanide the same as ferrocyanide? But if it is, what is the cation?

gainer · 05-10-2008, 01:53 PM

You could look them up in Wikipedia. The ferricyanide and ferrocyanide anions have the same number of iron, carbon and nitrogen atoms. The iron is ferric in one and ferrous in the other. The cation is usually potassium as we use it but could also be sodium or other elements for other uses. Ferricyanide is used in the blueprint process. If you get blueprint paper, you will have ferricyanide.

knoxissimpler · 05-10-2008, 02:59 PM

I thought it might be, but was not sure

also, the amount of paper ruined was around 500 sheets of Kodak polycontrast (they dont even make these anymore, and the guy here is on his last boxes) but mainly it is not for financial purposes, but for educational, and tests for practicality of methods of producing photo emulsion.

Illegible · 05-10-2008, 04:32 PM

It combines with water and makes lye.

gainer · 05-11-2008, 12:38 AM

Quote:

Originally Posted by Illegible

It combines with water and makes lye.

Yes, but the resulting solution could have equal numbers of NaOH and H(FeCN6) molecules. In use for bleaching, the balance is shifted to basic by adding a carbonate.

dancqu · 05-11-2008, 08:28 PM

Quote:

Originally Posted by Illegible

It combines with water and makes lye.

No one is going to make sodium. It is a most difficult
element to produce. High temperature electrolytic
methods I believe are used. Dan

Hologram · 05-12-2008, 12:28 AM

Quote:

Originally Posted by knoxissimpler

Hi, I have a large stack of photo paper that was ruined due to a classmate kicking open the single door to the darkroom... I tested the paper, and it is all ruined.

To some extent certain ultra-fine emulsions allow the erasure of previous light exposures.
So you might try to re-activate the emulsion: apply a mild Fe-EDTA bleach (say a 1% bleach solution during a couple of minutes) to get rid of the photolytic silver. Then for re-activation, put the paper in a 0.5% ascorbic acid bath for one minute.