How does Kallitype toning "work?"

[cirwin2010]

Out of curiosity I tried looking up how Platinum, Palladium, and gold toning Kallitypes (and other similar processes) work. I wasn't able to find much. I found a few references stating that "more noble metals will replaces less noble metals" in the print during toning, but nothing that seems to state how that works. I know that these metals don't form compounds with metallic silver like sulfur and selenium will. Some literature states that gold will "plate" the silver crystals in silver gelatin prints so how is it different when gold toning a Kallitype? Is this one of those things where it isn't well understood how this works?

 

[fgorga]

Disclaimer... I'm a (retired) bio/organic chemist with a spotty knowledge of inorganic chemistry.

All silver-based image are formed from metallic silver... Ag(0). The different silver-based processes yield different sized particles of Ag(0) which leads to differing tones in the final print. However, the toning of all of these processes is essentially the same.

Toning with noble metals [i.e. gold (Au), platinum (Pt) or palladium (Pt)] involves the following reaction (where X is one of the noble metals)...

Ag(0) + X+ ----> Ag+ + X(0)

In words the metallic silver is oxidized back to silver ions as the noble metal ions are reduced to their metallic form, X(0). This occurs on the surface of the image forming silver particles.

The result is some of the silver ends up back in solution and the X(0) is deposited onto the surface of the remaining Ag(0) particles.

Using your original descriptions "more noble metals will replaces less noble metals" and "gold will "plate" the silver crystals".

Hope this helps.

 

[cirwin2010]

Thanks for the reply! Yeah that helps and is what I was looking for. Is there a name for this particular type of reaction or would it just be classified as "oxidation?"

 

[fgorga]

Thanks for the reply! Yeah that helps and is what I was looking for. Is there a name for this particular type of reaction or would it just be classified as "oxidation?"

This is an oxidation-reduction reaction... often shortened to redox reaction.

Back in school, if you had a chemistry class, you might remember "LEO says GER"... LEO = Loss of Electrons - Oxidation and GER = Gain of Electrons - Oxidation.

An oxidation is always coupled to a reduction. The electrons lost from one species always end up being gained by some other species. The electrons lost in oxidation have to go somewhere!

 

[gbroadbridge]

Out of curiosity I tried looking up how Platinum, Palladium, and gold toning Kallitypes (and other similar processes) work. I wasn't able to find much. I found a few references stating that "more noble metals will replaces less noble metals" in the print during toning, but nothing that seems to state how that works. I know that these metals don't form compounds with metallic silver like sulfur and selenium will. Some literature states that gold will "plate" the silver crystals in silver gelatin prints so how is it different when gold toning a Kallitype? Is this one of those things where it isn't well understood how this works?

Have you looked at

MikeWare - Welcome

AlternativePhotography.com – Historical photographic methods in use today – the art, processes and techniques of alternative processes

www.alternativephotography.com

There is enough technical info there to challenge anyone