A New Cuprotype?

[Jan de Jong]

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.

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.

 

[Raghu Kuvempunagar]

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.

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.

 

[Jan de Jong]

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.

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

 

[Raghu Kuvempunagar]

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.

 

[AntonKL]

It seems that the exposure time of this process can be shortened down to classic cyanotype times by briefly heating the exposed print to >100°C before washing it, e.g. with a clothes iron with a sheet of paper in between.
I'm not using this process productively but rather was just trying to see if it works with my UV enlarger (no, the contrast is too low), and noticed that it gave more density with warm or even boiling water, then tried the clothes iron on a whim.
I made a comparison chart, using a printer test page on a transparency as step wedge, they came out a bit overexposed but the main point gets across nonetheless. For reference I also made a cyanotype print. The exposure was made with a 90W 395nm LED from ~10cm distance, hence the low times.
The unevenness in the prints comes from my poor coating job...

I also tried complex copper toning:

I used the recipes from Frank Gorgas Article and 125gsm "Canson 'C' a grain" drawing paper (it's nice for experiments since it dries really quick and washes easily, but I wouldn't use it for anything productive)

 

[Raghu Kuvempunagar]

Nice finding! The application of heat to the exposed print is making more Sulphide available (by breaking down Thiosulphate) to the formation of Copper Sulphide, I guess. A more acidic sensitiser/developer may help further, if you want to try, as Thiosulphate breaks down more easily in acid.

BTW @nmp @Jan de Jong and others: delighted to see Hypo-Cuprotype now being taught in wokshops.

Anne Eder

Showing the range of tones available with the cuprotype process. I’m a bit in love with this palette right now. Want to learn this? I have a workshop coming up in November with @lux.et.libera . DM me...

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