Jorge,
There is no reason to be concerned about questioning my statement that a palladium toned kallitype is physically the same as a straight palladium. I would assume that somebody would question a statement of this type and if I were wrong I would want to know so the discussion is really very useful. However, I still believe I am right in that there is no essential physical difference between these two types of images. However, your comments about completion raise some questions as to whether the replacement of silver by gold, palladium or platinum can b e 100%. But the fact that a palladium toned platinum is visually identical to a straight palladium suggests to me that the percentage of replacement is extremely high, and if it is indeed very high it seems reasonable to believe there is the possibility that it might go to completion.
For what it is worth I agree with both you and Michael that if the replacement is not 100% we should not label a palladium toned kallitype as a palladium.
The formula given in the earlier message is from Grant Haist’s Modern Photographic Processing, Vol. 2, p. 122. Grant Haist was a senior research scientist at Eastman Kodak in Rochester for many years and this book is in my opinion the most authoritative work ever published on photographic processing.
I think you have a good point when you write, "Unless the optical density of gold is much greater than that of silver . . . you would run out of silver way before you have deposited enough gold in those sites to give the same tone" Haist himself mentions that the difference between the amount of gold deposited when gold is in its aurous state, which is about three times as much as deposited in the aurici state, is a result of the two oxidation states of gold. In practice you will indeed find that when a kallitype print is toned to completion with gold the final image is significantly lighter than before toning. With palladium and platinum toning, however, there is no loss of density. To the contrary, there is a slight gain in density.
Platinum and palladium toning of silver gelatin prints was very rarely done in the 20th century and Haist does not indicate how the process of metal replacement takes place. Perhaps someone with experience in metal chemistry can provide guidance on this issue.
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