A blended ferrocyanide print process

Raghu Kuvempunagar · Apr 5, 2025

Thanks for the clarifications.

I'll try to replicate at my end when I get a chance hopefully soon.

PGum · Apr 5, 2025

I haven’t made cuprotypes in a while but in my last prints, I pre-coated the paper with a neutral 10% sodium citrate solution, then let dry. This reduced highlight staining significantly. However, I wasn’t using a development bath other then water. The formula I used was more along the lines of Cor Breukel’s approach.

Raghu Kuvempunagar · Apr 6, 2025

PGum said:
I haven’t made cuprotypes in a while but in my last prints, I pre-coated the paper with a neutral 10% sodium citrate solution, then let dry. This reduced highlight staining significantly. However, I wasn’t using a development bath other then water. The formula I used was more along the lines of Cor Breukel’s approach.

That's a great idea! The developer already has a lot of citrate and hence I didn't consider the possibility of adding it to the sensitiser or coating the paper with it prior to sensitisation as you have suggested. It could also interfere with the cyanotype exposure possibly. Nevertheless I should give it a try.

Thanks.

Debanjan · Tuesday at 4:54 AM

I also wanted to update this thread with another discovery related to this process.. I was exposing for approximately 150 - 160% of my Cyanotype exposure timings to get the previous 2 examples I shared here. With normal Cyanotype exposure times, I see that the Copper-Brown dominates the print with virtually no trace of Prussian Blue -- something similar to a Salt Print .. so the toning possibilities are quite a lot with this process but we need proper calibration and some degree of standardisation.

Both the prints are on Canson Montval paper. Size is A4

koraks · Tuesday at 5:20 AM

@Debanjan that's interesting; what fascinates me most is the apparently brown hues you're getting with this. I recognize that if you dial back exposure a little, all you get is the copper image without the cyanotype/Prussian Blue part. You'll see this reflected in my examples in post #85. However, in my case, the hues are pink-orange, not brown, and overall density of the copper is much lower than what they look like in your prints. Can you tell us a little more about your process?

Debanjan · Tuesday at 6:07 AM

@koraks - I followed the process suggested by the OP. Since both @Raghu Kuvempunagar and I have almost identical UV box set-up, in order to compensate for the lower sensitivity of the brown FAC, I started with 150-160% of the normal Cyanotype timing. The paper was given a mild citric acid bath and wash to get rid of the buffers. However, I wanted to test the outcome with my normal timings and this was the result. I will redo a series of step charts to check this variation since the one I did a couple of days back was not definitive enough ..

Raghu Kuvempunagar · Tuesday at 8:27 AM

Nice work @Debanjan! Thanks for sharing.

The brown we see here is indeed a combination of Copper Ferrocyanide and Prussian Blue. The presence of PB can be tested by reducing the print with either Ascorbic Acid or FAC+UV light. You can notice the change in hue after reduction.

Debanjan · Tuesday at 9:39 AM

Raghu Kuvempunagar said:
Nice work @Debanjan! Thanks for sharing.

The brown we see here is indeed a combination of Copper Ferrocyanide and Prussian Blue. The presence of PB can be tested by reducing the print with either Ascorbic Acid or FAC+UV light. You can notice the change in hue after reduction.

Let me try out and report the outcomes..

Andrew O'Neill · Tuesday at 10:00 AM

One important variable... I went a few days with disastrous results, (uneven blotchy coatings, coatings that took forever to dry, staining, leaching, zero tone) until finally cluing in in to what the problem was. Room RH. I hadn't realised that my dehumidifier was off, allowing the RH to rise to 90 and room temp down to 15C. Once I got the RH down to 60 and room temp up to 20, Bob's your uncle.

koraks · Tuesday at 10:23 AM

Andrew O'Neill said:
Once I got the RH down to 60 and room temp up to 20, Bob's your uncle.

Funny you should mention that. I now recall that on my first day of testing, I tried exposing humid paper. The results were horrible, indeed - worse than I had been getting otherwise. I touched base with @Raghu Kuvempunagar to check how he dried his sensitized paper and he said he blasts them dry with a hairdyer at high heat - exactly what I normally do, too. So I went back to doing that and proceeded with other aspects of problem solving. At least I can confirm that drying the sensitized paper thoroughly doesn't hurt and probably helps along as well. The print-out image is different (stronger) when exposing humid paper.

Andrew O'Neill · Tuesday at 3:00 PM

I tried some old Stonehenge paper that I had laying around. Cheap and thin. I forgot how crappy this paper is for Alt. Anyways, I went ahead and acidified it in 10% Sulfamic Acid, washed and hung up to dry. Now the crappy part that I had forgotten about... it doesn't like brush application. To be more accurate, it doesn't like foam brush application. Small paper burrs on the surface. Once the paper dried, I was able to brush them off with my hand. I made the exposure, and developed in the Copper Sulphate...by brushing it on with a foam brush. More burrs. But... I got a wonderful print! Much better than what I could get on expensive, Revere. So... I acidified a sheet of the Revere, even though one would think that it's not buffered like these cheap papers, but what the heck. I'm waiting for the Cyanotype coating to dry, then I'll give it a go. For now, here is the print on cheap garbage Stonehenge... You can see the paper burrs on the full print. I included a closeup, too...

Andrew O'Neill · Tuesday at 3:01 PM

I forgot to say that the above was made from a digital negative. Up until now, I have been using the actual XRAY negative.

Raghu Kuvempunagar · Tuesday at 10:37 PM

Andrew O'Neill said:
it doesn't like brush application. To be more accurate, it doesn't like foam brush application. Small paper burrs on the surface.

I had similar bad experience with foam brush earlier when I used them to coat Cyanotype on some cheap local watercolour papers. With a colloid like gelatin added to the sensitiser, they were fine.

I use cheap brushes similar to this: https://www.amazon.com/Stationerie-Artists-Hake-Watercolour-Brush/dp/B0CM5VM7P4/?th=1

Works without a problem even for coating bond paper.

Your print has a lot of pinhole artifacts. What are those?

Andrew O'Neill · Tuesday at 10:58 PM

@Raghu Kuvempunagar Not pinholes. They are paper burrs caused by the foam brush.

Raghu Kuvempunagar · Wednesday at 4:14 AM

koraks said:
The resulting prints I've made so far on critical examination show no signs of any conversion/capture of copper into a ferro/ferri-based compound. They really just show a copper nanoparticle fog overlayed on top of a cyanotype print. I've a feeling I'm missing something very crucial, but re-reading your process steps I can't seem to put my finger on it.

If you PM me your address, I'll get some sheets of paper in the mail so you can play with them; don't worry about payment, I expect none.

Yesterday I received a few sheets of Schut papers from Netherlands for testing. Thanks @koraks, much appreciated!

As these papers have given @koraks and @Cor varying degree of problems that I didn't fortunately encounter with the limited brands of papers I used in my work, I cut one of the Schut Salland sheets into two halves and used one of them with a lot of trepidation for testing. I wanted to see what issues I would encounter with Schut Salland paper, so I didn't give the sheet an acid pre-wash. Nor did I add any Ammonium Chloride to the sensitiser as I would do for papers that can't be given acid pre-wash. I coated, exposed and developed normally bracing for imminent failure.

Here is the print after drying:

While taking the picture of the print, I overlaid it on the other half of the Schut Salland sheet. This should give you a good idea of the stain, talking of which I didn't manage to produce it in the prodigous amounts seen in the prints here.

The colour palette in the print might not be everybody's favourite, but I think the print came out very decent. Most importantly, the paper seems to be unproblematic for this process, in my setting at least, quite unlike what was reported here.

Now, why such noticeable divergence in the results with the same paper, I've no idea. Could be the quality of the chemicals or other variables.

koraks · Wednesday at 4:18 AM

Thanks so much for testing this @Raghu Kuvempunagar and I'm thrilled to see that beautiful print on this paper! It looks great to my eye - yes, there's probably still some fog, but it's quite in line with the more recent attempts I did, which come out comparably clean. However, in my case, that's with additional measures such as adding ammonia or chloride ions. I'm surprised to see the paper perform so well without these measures. I also note that the color palette is still much more to the yellow/tan side in Raghu's print than the pink/salmon hues I get on the highlight/copper image.

The question now remains indeed what factor accounts for these differences. To be honest, I'm at a loss.

Cor · Wednesday at 5:01 AM

I did some testing on the Schut paper, adding different chemicals to the developer.

Conditions:

Digital negative (may or may not be optimal, but I am happy with the results
Schut paper (size A4)
3 ml sensitizer solution (foam brush): all in one solution which after 4 days became increasingly hard to get an even coat (you see coating artifacts in below scan) with Ammonium Chloride, will go back to the 2 solution option (AFC+Amm. Cl and KFeCN)
12 minutes exposure on my UV bank
Developer:
Top: 1 ml Copper stock + 3 ml 20% KBr
Middle: 1 ml Copper stock + 0.5 ml 0.5 M EDTA (=0.084 gram) +2.5 ml water
Bottom: 1 ml Copper + 3ml Sodium Citrate

After exposure the different developers are brushed on and kept there for 1-2 minutes, the EDTA one takes longer (chelating the metals).

Below image is from the still wet prints and give a approximate impression of the different colours possible. I would say it is quite flexible! Still no pure paper white in these images, but the Sodium Citrate seems to be the brightest, and on a stepwedge is give almost pure paper white in the higher steps.

Best,

Cor

koraks · Wednesday at 5:15 AM

Cor said:
but the Sodium Citrate seems to be the brightest

The middle one looks the cleanest to me, and I understand that's the one with EDTA added to the developer, correct? I wonder how that would look if you leave it to develop longer, and/or reduce the EDTA concentration to a threshold amount that just suppresses fog without hampering development too much. It'd require some experimentation to determine that amount (if there actually is such a threshold concentration).

Cor · Wednesday at 5:39 AM

Dialing the EDTA is a bit finicky, to little there is fog on all steps in the stepwedge, too much there is no copper ferrocyanide at all, as expected since EDTA will chelate (bind) all the copper ions.

At this point I like the sodium citrate the best, is has a nice Dmax and a nice image tone. The EDTA one is clear blue in the shadows and that switches to the salmon/orange of the copper ferrocyanide, I like this less for these images.

Best,

Cor

Andrew O'Neill · Wednesday at 6:41 PM

I was able to make a decent print, using the traditional cyanotype recipe, on Revere paper. I'll just do it this way so that I don't have umpteen different concoctions laying around... And I can still make straight cyanotypes when needed!

NedL · Wednesday at 8:31 PM

Andrew O'Neill said:
I was able to make a decent print, using the traditional cyanotype recipe, on Revere paper. I'll just do it this way so that I don't have umpteen different concoctions laying around... And I can still make straight cyanotypes when needed!

Interesting... no excess pot ferri. I'm going to try soon... will start w/ OP recipe.

Andrew O'Neill · Wednesday at 10:13 PM

koraks · Thursday at 2:25 AM

I don't see a lot of gradation to the copper image in that one, @Andrew O'Neill . It looks nice as it is, but it's not a FerroBlend print, technically speaking. It's a cyanotype with a constant copper-toning layer on top of it.

Raghu Kuvempunagar · Thursday at 2:36 AM

@koraks: you're right. It seems more like a layer of CF has been added on top of regular Cyanotype image.

@Andrew O'Neill: can you please share pics of the print at intermeidate stages? Will help us understand what's happening. And does your developer contain Citrate as specified in OP?

Andrew O'Neill · Thursday at 10:37 AM

Yes, there is Sodium Citrate in the developer. The only thing I did different here is that I used the straight Cyanotype recipe. I'll revisit all of this after I get back from Japan in June. I'm too busy now. Thanks!

A blended ferrocyanide print process

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