A New Cuprotype?

Raghu Kuvempunagar said:

That's an interesting idea though I'm unable to fathom what ferricyanide and ferrocyanide do to reduce stain. However, tartaric acid could potentially help as it is copper chelate. I didn't add dichromate as restrainer in the sensitiser and on hindsight I should have.

For intensifying, in a different test, I have tried developing in copper sulphate + tartrate + thiocyanate and it seems to work (sample size = 1). But I didn't do more tests because developing in a thiocyanate broth defeats the purpose of adding thiocyanate to the sensitiser. Your idea of toning in ferricyanide + ferrocyanide + tartaric acid could potentially help if the plain ferricyanide developer isn't converting all copper(i) thiocyanate to copper(i) ferrocyanide. John Mercer used ammonium chloride with ferricyanide in his experiments to convert copper(i) thiocyanate to copper(i) ferrocyanide. That could be another avenue if I were to redo this experiment again.

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I thought it was an interesting observation and surprised me to see such whites. I could quote what CoPilot (now has renamed itself to Ferra in my conversations) tells me. It says Kferro could act as a mild complexing agent and binding stray Cu2+ ions, where the tartaric acid lowers the pH which keeps the copper ions moure soluble and may prevent precipitation of hydroxides and oxides.
I would have to try again to repeat to see if the observation is repeatable. I was hoping you may have some scraps left to confirm.

Jan de Jong said:

I thought it was an interesting observation and surprised me to see such whites.
I would have to try again to repeat to see if the observation is repeatable. I was hoping you may have some scraps left to confirm.

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It is indeed an interesting observation. Unfortunately, I don't have ferrocyanide at the moment and it won't be before October I can get new chemicals. I'll remember and give the ferri+ferro+tartaric mixture a try when I get the chance.

Raghu Kuvempunagar said:

It is indeed an interesting observation. Unfortunately, I don't have ferrocyanide at the moment and it won't be before October I can get new chemicals. I'll remember and give the ferri+ferro+tartaric mixture a try when I get the chance.

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you can reduce some KFerri to KFerro in a simple way though

Jan,

I'm reluctant to use ascorbic acid (or any acid) with ferricyanide. So I tried the following:

Solution A
Water: 10 ml
Potassium ferricyanide: 0.2 g
Sodium sulphite: 0.1 g
Potassium ferricyanide: 0.2 g

Solution B
Water: 10 ml
Tartaric acid: 0.2 g
Sodium carbonate: just enough to get pH ~6

Add solution B to A and stir well.

I brushed this mix over a cuprotype print, left the print untouched for 10 minutes, washed in dilute citric acid followed by normal water wash.

I didn't notice any intensification of the darks or lightening of the lighter tones unfortunately.

Sulphite reduces ferricyanide to ferrocyanide and hence solution A is a mix of both ferricyanide and ferrocyanide. There is also some sulphate in it due to the oxidation of sulphite. And pH is higher than your mix. No idea if these differences played any role.

I will get some ferrocyanide in the near future and give it a try as I remain intrigued by the possibility of contrast increase.