A new cyanotype toning method?

xiaruan · Apr 7, 2025

我想我可能发现了一种新的蓝晒调色方法。我用硫酸铜来调蓝晒法。
我已经在其他帖子中讨论过这个问题，但我相信这种方法值得专门讨论。

https://www.photrio.com/forum/threads/showcase-for-your-hcwps.199853/page-31#post-2885917

您需要什么：

漂白液：6g 柠檬酸钾 + 6g 抗坏血酸溶于 50mL 蒸馏水中。这种溶液可以将普鲁士蓝还原为普鲁士白。
调理液：15g 柠檬酸钾 + 5g 硫酸铜溶于 50mL 蒸馏水中。该溶液将普鲁士白转化为亚铁氰化铜（I）。
氧化液：向水中加入约 3% 的双氧水（量可自由调整）。这会将亚铁氰化铜（I）氧化成亚铁氰化铜（II）。

实验程序：

将完成的蓝晒法浸泡在漂白溶液中 5 分钟，直到图像完全变白。
用水冲洗纸张以去除残留的漂白溶液。
将纸张浸泡在调色液中 5 分钟（如果需要，可以更长时间）。
取出纸张后，将其放入氧化液中以显出红色。

实验结果如下：

这种方法也可能适用于其他过渡金属。

xiaruan · Apr 7, 2025

AndrewBurns said:
I took the liberty of putting the above through google translate, so I hope this translation is correct:

I think I may have discovered a new method for cyanotype tinting. I use copper sulfate for cyanotype tinting.
I have discussed this in other posts, but I believe this method deserves a separate discussion.

Showcase for Your HCWP's

Learn something new every day! I knew about potassium oxalate but I didn't know about this. Thanks, something new to try sometime! I would think sulfite works like an alkali - as in bleaching, although more gently than sodium carbonate etc. Sodium/potassium oxalate, citrate etc actually...

www.photrio.com

What you need:

Bleaching solution: 6g potassium citrate + 6g ascorbic acid dissolved in 50mL distilled water. This solution will reduce Prussian blue to Prussian white.
Conditioning solution: 15g potassium citrate + 5g copper sulfate dissolved in 50mL distilled water. This solution will convert Prussian white to copper ferrocyanide (I).
Oxidizing solution: Add about 3% hydrogen peroxide to water (the amount can be adjusted freely). This will oxidize copper ferrocyanide (I) to copper ferrocyanide (II).

Experimental Procedure:

Soak the finished cyanotype in bleach solution for 5 minutes until the image turns completely white.
Rinse the paper with water to remove the remaining bleach solution.
Soak the paper in the toner for 5 minutes (or longer if necessary).
After removing the paper, place it in an oxidizing solution to bring out the red color.

The experimental results are as follows:

Thank you for your translation. Due to my browser's auto-translate feature, my original post was automatically translated into Chinese.

xiaruan · Apr 7, 2025

Here is the original content.

I think I may have discovered a new cyanotype toning method.I used copper sulfate to tone the cyanotype.
I've discussed this in other threads, but I believe this method deserves its own dedicated discussion.

A blended ferrocyanide print process

I also had to add Ammonium Chloride to Part A, as the Cyanotype was lifting off from the paper. In my experiments I used 4% gelatin with 0.2% glutaraldehyde to stabilize* the cyanotype layer see (in English) Variant 1 in https://illumina-chemie.org/viewtopic.php?p=72786#p72786 with the...

www.photrio.com

What you need:

Bleaching solution: 6g potassium citrate + 6g ascorbic acid dissolved in 50mL distilled water. This solution can reduce Prussian blue to Prussian white.
Toning solution: 15g potassium citrate + 5g copper sulfate dissolved in 50mL distilled water. This solution converts Prussian white into copper(I) ferrocyanide.
Oxidation solution: Add some 3% hydrogen peroxide to water (amount can be adjusted freely). This oxidizes copper(I) ferrocyanide into red copper(II) ferrocyanide.

Experimental procedure:

Soak the finished cyanotype in the bleaching solution for 5 minutes until the image turns completely white.
Rinse the paper with water to remove residual bleaching solution.
Soak the paper in the toning solution for 5 minutes (or longer if needed).
After removing the paper, place it in the oxidation solution to develop the red color.

This method might also be applicable to other transition metals.

koraks · Apr 8, 2025

Thank you @xiaruan for making this technique accessible to all of us! I will move this thread to the Alternative Printing Processes subforum in a minute, where it fits a little better.

mshchem · Apr 8, 2025

Thanks for sharing your work!

Raghu Kuvempunagar · Apr 8, 2025

@xiaruan: very interesting idea! I gave this idea a try (well.. three tries actually). But I think I need your help in figuring out if I am missing something. I followed the steps given in your post and couldn't get the reddish brown colour that you got.

Cyanotype:

After reduction with Ascorbic Acid (+Citrate) and subsequent wash to remove residual Ascorbic Acid:

The print was much paler than seen above immediately after bleaching. However, the subsequent wash brought back some of the blue as expected (PW gets oxidised to PB by air in the presence of water).

After treating with Copper Sulphate + Citrate:

I gave a good wash to remove residual Copper Sulphate from the print after the above step. Next I cut the print into two halves - treated one with Hydrogen Peroxide and the other with Potassium Ferricyanide. Here are the results after oxidation, wash and drying:

Peroxide treated one is at the bottom and Ferricyanide treated one is at the top. Notice that neither of them have the yellowish brown tone seen in your tests. Since I got very similar results in three attempts, I am at loss about what I missed in the steps detailed by you.

BTW you might be interested in a previous work that claims to have "converted" a Cyanotype print into a Cuprotype print:

It works as follows: a cyanotype [is] immersed for a few minutes in a 1% solution of copper sulfate followed by bleaching the "copper sulfate" print and then immersing it in a potassium ferrocyanide solution. From the little I understood of the underlying mechanism, the idea seems to be along the lines of traditional Cyanotype toning - bleach the Cyanotype print with Sodium Carbonate and add a layer of Copper Ferrocyanide pigment formed in situ by the reaction between Copper Sulphate and Potassium Ferrocyanide. I would think that by bleaching partially a more interesting colour palette can be achieved.

xiaruan · Apr 8, 2025

Raghu Kuvempunagar said:
After reduction with Ascorbic Acid and subsequent wash to remove residual Ascorbic Acid:

It appears there may have been an issue with the bleaching process, as your results show no noticeable effect. I used a mixture of ascorbic acid and potassium citrate as the reducing agent, which can rapidly and completely bleach the image to near invisibility—this may be related to the potassium citrate in the formulation.

Raghu Kuvempunagar said:
It works as follows: a cyanotype [is] immersed for a few minutes in a 1% solution of copper sulfate followed by bleaching the "copper sulfate" print and then immersing it in a potassium ferrocyanide solution. From the little I understood of the underlying mechanism, the idea seems to be along the lines of traditional Cyanotype toning - bleach the Cyanotype print with Sodium Carbonate and add a layer of Copper Ferrocyanide pigment formed in situ by the reaction between Copper Sulphate and Potassium Ferrocyanide. I would think that by bleaching partially a more interesting colour palette can be achieved.

This is indeed an intristing study, but it appears to follow a fundamentally different mechanism compared to my approach.

koraks · Apr 8, 2025

xiaruan said:
this may be related to the potassium citrate in the formulation

Yes, I also noticed the absence of citrate in @Raghu Kuvempunagar's writeup.
Btw, is the use of potassium citrate essential, or do you expect sodium citrate to also work?

Raghu Kuvempunagar · Apr 8, 2025

Thanks for the quick response @xiaruan. As I wrote in my earlier post, the print after bleaching in Ascorbic Acid is quite pale in colour, but it gets back some of the blue immediately after washing in water to remove the residual Ascorbic Acid. This is quite expected because PW is oxidised partially by air and water and happens even when a Cyanotype print is water developed after exposure. As far as Potassium Citrate is concerned, I used Sodium Citrate in about the same amount mentioned in your post. Do you think Potassium Citrate is absolutely critical and Sodium Citrate wouldn't be a functional substitute? In any case, the print after oxidation with peroxide doesn't show any hint of of Copper Ferrocyanide. So I am at loss what could have prevented the toning even partially. I'll give another try if I can think of something or wait till others have tried and learn from their experiences.

Regarding the reddit work that I shared, you're absolutely right. Its mechanism is different from yours but is a plausible root to forming Copper Ferrocyanide starting with a finished Cyanotype print.

koraks said:
Yes, I also noticed the absence of citrate in @Raghu Kuvempunagar's writeup.
Btw, is the use of potassium citrate essential, or do you expect sodium citrate to also work?

I used Sodium Citrate in both bleach and Copper Sulfate toner. Will edit my earlier post to reflect this.

xiaruan · Apr 8, 2025

koraks said:
Btw, is the use of potassium citrate essential, or do you expect sodium citrate to also work?

Theoretically, both sodium and potassium ions can act as stabilizers for Prussian white, but potassium ions likely demonstrate superior stabilization effects.

xiaruan · Apr 8, 2025

Raghu Kuvempunagar said:
Thanks for the quick response @xiaruan. As I wrote in my earlier post, the print after bleaching in Ascorbic Acid is quite pale in colour, but it gets back some of the blue immediately after washing in water to remove the residual Ascorbic Acid. This is quite expected because PW is oxidised partially by air and water and happens even when a Cyanotype print is water developed after exposure. As far as Potassium Citrate is concerned, I used Sodium Citrate in about the same amount mentioned in your post. Do you think Potassium Citrate is absolutely critical and Sodium Citrate wouldn't be a functional substitute? In any case, the print after oxidation with peroxide doesn't show any hint of of Copper Ferrocyanide. So I am at loss what could have prevented the toning even partially. I'll give another try if I can think of something or wait till others have tried and learn from their experiences.

Regarding the reddit work that I shared, you're absolutely right. Its mechanism is different from yours but is a plausible root to forming Copper Ferrocyanide starting with a finished Cyanotype print.

I used Sodium Citrate in both bleach and Copper Sulfate toner. Will edit my earlier post to reflect this.

It's possible that the water used to rinse the reducing agent contains excessive oxidants. You might consider proceeding directly to the next step without rinsing the reducing agent.

Raghu Kuvempunagar · Apr 8, 2025

xiaruan said:
It's possible that the water used to rinse the reducing agent contains excessive oxidants. You might consider proceeding directly to the next step without rinsing the reducing agent.

The oxidant in the rinse water is oxygen. But your suggestion to skip the water rinse makes sense as it will make available as much PW as possible to the toner. I will give it a try when I get the opportunity to do further testing.

xiaruan · Apr 9, 2025

Raghu Kuvempunagar said:
The oxidant in the rinse water is oxygen.

The oxidants in the rinse water may not necessarily be oxygen. Municipal tap water often contains excess oxidants added during treatment to prevent microbial contamination in pipelines, which could lead to elevated oxidant levels. To mitigate this, you may let the tap water stand for a period before use.

xiaruan · Apr 20, 2025

Raghu Kuvempunagar said:
Do you think Potassium Citrate is absolutely critical and Sodium Citrate wouldn't be a functional substitute?

The sodium citrate I ordered finally arrived today. I tried replacing potassium citrate with sodium citrate in the formula, but it turns out potassium citrate is essential.

In the image above, the beaker on top contains sodium citrate and ascorbic acid, while the one below holds potassium citrate and ascorbic acid. It is evident that the sample in the lower beaker appears significantly whiter. Additionally, the bleaching process was observed to proceed at a remarkably rapid rate.

In this image, the left side shows the staining with sodium citrate and copper sulfate, while the right side demonstrates the result after adding a small amount of potassium citrate to the staining solution. It can be observed that sodium citrate and copper sulfate alone fail to convert Prussian white into copper(I) ferrocyanide.

xiaruan · Apr 20, 2025

Therefore, I conclude that potassium citrate is indispensable in this formulation.

Andrew O'Neill · Apr 20, 2025

I'm taking all this in while sitting on a slow train, somewhere in the Japanese countryside, unable to give this a go!

Raghu Kuvempunagar · Apr 20, 2025

xiaruan said:
The sodium citrate I ordered finally arrived today. I tried replacing potassium citrate with sodium citrate in the formula, but it turns out potassium citrate is essential.

That's really very sweet of you to have tested the process with Sodium Citrate! Thank you so much. I am not a chemist and I hope someone with more chemistry knowledge than me can explain the different behaviour of your process wrt to Cations. I would also love to know the reaction path from Prussian White to Copper(II) Ferrocyanide.

I'll definitely give the process another try in the future as soon as I get an opportunity. In the meanwhile I'll be watching this thread for further updates from you and others.

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