How does Kallitype toning "work?"

cirwin2010 · Aug 22, 2025

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 · Aug 22, 2025

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 · Aug 22, 2025

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 · Aug 22, 2025

cirwin2010 said:
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 · Aug 22, 2025

cirwin2010 said:
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

koraks · Aug 23, 2025

cirwin2010 said:
Is there a name for this particular type of reaction

In addition to what @fgorga mentions about this being in the scope of redox reactions in chemistry, I've seen this referred to in a photographic context as 'metal replacement toning'. Eg. here: https://en.wikipedia.org/wiki/Photographic_print_toning#Metal_replacement_toning

cirwin2010 · Monday at 4:46 PM

I have another similar question that one of you smart folks can help me with. In the context of redox reactions, what is the correct order of reactivity of the following elements: Pt, Pd, and Au?

I have read through "Kallitype, Vandyke Brown, and Argyrotype" by Don Nelson. In one of the chapters he has a short mention of double toning Kallitypes with Platinum, Palladium, and gold. He states that Pt and Pd are more noble than Au and will not be replaced by Au. If you tone with Au first then it will be replaced by Pt or Pd.

I tried this with a Kallitype that I first toned with Pd until it stated looking a dark brown in color. I then put it in my gold toner (231) bath after a rinse. This turned the print a blue black color much like if I had only used the gold toner exclusively. I did not get the warm highlights that Don's book suggested I should have been able to achieve.
This lead me down a rabbit hole of trying to understand the reactivity series of metals. Some sources seem to suggest that Pt would more readily give up its electrons than Au. I assume Pt is "more noble" than Pd so I would also assume this to mean that Pd is more reactive than Au. This contradicts the author of my book so I'm looking for clarity. I am also seeing contradictory information online regarding if Pt is more reactive than Au (or vice-versa) hence why I would want to consult someone with a better understand of chemistry than I.

gbroadbridge · Monday at 5:02 PM

I don't know if the exact answer you are looking for is there, but have you looked at the free book downloads on Dr Mike Wares site?

mikeware.co.uk

revdoc · Tuesday at 2:22 AM

As far as "which should be used first", I've seen references to gold toners for platinum prints, which implies that gold should be done before platinum. Presumably that applies to palladium as well.

cirwin2010 · Tuesday at 9:39 AM

I'm seeing a few vague referencing online about gold toning platinum/palladium prints. So that is possible? If so I think that proves that the information in the book is incorrect, yes?

fgorga · Tuesday at 10:27 AM

revdoc said:
As far as "which should be used first", I've seen references to gold toners for platinum prints, which implies that gold should be done before platinum. Presumably that applies to palladium as well.

cirwin2010 said:
I'm seeing a few vague referencing online about gold toning platinum/palladium prints. So that is possible? If so I think that proves that the information in the book is incorrect, yes?

Both of these posts are correct.

The reason, as one might suspect, is in the details of the redox chemistry.

The propensity to donate or accept electrons is measured by the 'standard electrode potential' which is typically measured in volts.

Here are the values for the metals in question

Au -- 1.5
Pt -- 1.19
Pd -- 0.92
Ag -- 0.80

A metal with a higher potential can be used to replace one with a lower potential.

Thus, gold (Au) can be used to tone prints made with any of the other metals under discussion.

Furthermore, if one gold tones a print already toned with platinum (Pt) or palladium (Pd) the gold will replace the Pt/Pd thereby 'undoing' the first toning.

With split toning the devil is in the details, one needs to pay careful attention to both the concentration of the toners, the time prints stay in the toning bath and the temperature if one wants to have reasonably consistent split toning.

Split toning results will depend on the extent of gold toning since the subsequent toning with Pt or Pd will depend on how much residual silver is present after the gold toning.

Tom Taylor · Tuesday at 11:25 AM

I may have this backwards but I believe that gold tones from the bottom (shadows) up and platinum from the top down. Here is a kallitype that I split-toned with gold and platinum:

cirwin2010 · Tuesday at 12:52 PM

fgorga said:
Both of these posts are correct.

The reason, as one might suspect, is in the details of the redox chemistry.

The propensity to donate or accept electrons is measured by the 'standard electrode potential' which is typically measured in volts.

Here are the values for the metals in question

Au -- 1.5
Pt -- 1.19
Pd -- 0.92
Ag -- 0.80

A metal with a higher potential can be used to replace one with a lower potential.

Thus, gold (Au) can be used to tone prints made with any of the other metals under discussion.

Furthermore, if one gold tones a print already toned with platinum (Pt) or palladium (Pd) the gold will replace the Pt/Pd thereby 'undoing' the first toning.

With split toning the devil is in the details, one needs to pay careful attention to both the concentration of the toners, the time prints stay in the toning bath and the temperature if one wants to have reasonably consistent split toning.

Split toning results will depend on the extent of gold toning since the subsequent toning with Pt or Pd will depend on how much residual silver is present after the gold toning.

Thanks for clearing that up! Between your explanation and what I witnessed for myself I can conclude that the author of my book got some information backwards. Now whether I can articulate any of this well enough in an email to the author is another question.

cirwin2010 · Tuesday at 12:56 PM

Tom Taylor said:
I may have this backwards but I believe that gold tones from the bottom (shadows) up and platinum from the top down. Here is a kallitype that I split-toned with gold and platinum:

View attachment 409005

Visually, gold tones from the highlights down. This was very apparent when toning some step wedges for calibration purposes. The effect can be quite strong if the print is pulled early when using a "brown" developer with 231 gold toner for Kallitypes. You would get blue-black highlights and brown shadows.

With my particular process, platinum and palladium appear to tone relatively evenly across the print. I cannot pick out if highlights or shadows are effected first.

koraks · Tuesday at 1:52 PM

Tom Taylor said:
gold tones from the bottom (shadows) up and platinum from the top down.

I've never found a satisfactory theoretical explanation for this, nor have I been able to demonstrate it. Toners affect the metallic image. They don't care at what part of the curve that metal happens to be.

I think what likely happens is that with some toners, we more easily see the change in hue in the highlights, while with other hues, the shadow changes are more apparent at first. This phenomenon then might have found its way into common parlance, confusing the subjective impression with a physical/chemical mechanism. I think the two should not be confused, especially not in the context of this specific question.

cirwin2010 · Tuesday at 2:05 PM

koraks said:
I've never found a satisfactory theoretical explanation for this, nor have I been able to demonstrate it. Toners affect the metallic image. They don't care at what part of the curve that metal happens to be.

I think what likely happens is that with some toners, we more easily see the change in hue in the highlights, while with other hues, the shadow changes are more apparent at first. This phenomenon then might have found its way into common parlance, confusing the subjective impression with a physical/chemical mechanism. I think the two should not be confused, especially not in the context of this specific question.

This is my understanding as well. All areas are effected equally, but depending on the toner (or bleach) certain areas will show color change before others due to the density thus giving the illusion that highlights or shadows are affected first.

koraks · Tuesday at 2:08 PM

Yes, precisely; I can also see how this visual effect can easily be mistaken for a differential rate in physical metal replacement, but as said, I've never seen good empirical or theoretical support for this.

How does Kallitype toning "work?"

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