harvesting silver from over-exposed paper

[gainer]

How would I want to use that? what form of iodine is it? Where on the activity series is Iodine compared to silver?

I didn't say one should use water purification tablets for anything but purifying water. In fact, I was trying to say that I thought the hypochlorite might be accidentally formed while trying somehow to use elemental chlorine to form the silver chloride, and that would be a bad thing, because it would damage if not destroy the gelatine emulsion. So, DO NOT use either form of water sterilization tablets in this process.

 

[gainer]

To sum up, my suggestion would be to develop your paper in a strong print developer with the room light on so that it turns as black as it will go. Wash it thoroughly, bleach it under red light in the ferricyanide + potassium bromide or chloride solution, wash and dry it (still in dark or safelight) and see if you can use it as contact printing paper.

 

[knoxissimpler]

To sum up, my suggestion would be to develop your paper in a strong print developer with the room light on so that it turns as black as it will go. Wash it thoroughly, bleach it under red light in the ferricyanide + potassium bromide or chloride solution, wash and dry it (still in dark or safelight) and see if you can use it as contact printing paper.

what is the prupose of the ferricyanide? (FYI, I do not like to mess with cyanide, with a couple exceptions)

 

[GeoffHill]

Wow, if youre going to do all this work, it must be for quite a pile of paper. How much paper did you fog?

 

[gainer]

what is the prupose of the ferricyanide? (FYI, I do not like to mess with cyanide, with a couple exceptions)

Ferricyanide, usually the potassium compound, IS the bleaching agent most often used.

FYI, ferricyanide is not cyanide. If you use Farmer's Reducer or the bleach-redevelop method of sulfide toning, you are probably using ferricyanide. It is used in many photographic processes. Perhaps one of the professional chemists in our group will explain the difference and the necessary precautions for unusual use. It is not the same as potassium or sodium cyanide, which will generate HCN gas even in mildly acidic solution.

 

[Kirk Keyes]

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]

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

 

[gainer]

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]

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]

where would the sodium go?

It combines with water and makes lye.

 

[gainer]

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]

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]

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.