This is a long post, but it may be of interest to Cyanotype and Cuprotype practitioners. I describe a process that has yielded satisfying results and is almost as simple as the Cyanotype process. If you get a chance, please try it and share your results and experiences. Your feedback would be highly valuable to me.
— Raghu
Motivation
Cyanotype and Cuprotype are two popular printmaking processes that offer inexpensive and versatile alternatives to silver-based methods. However, both are limited in the range of colour tones they can produce. As the pigment that constitutes the image is a ferrocyanide in both Cyanotype and Cuprotype processes, I became interested in the possibility of a printing process in which the image is formed by a blend of ferrocyanides. Such a process would be interesting to me and many others because the colour tone of the image would be very different from the familiar blue of Cyanotype and the reddish brown of Cuprotype. This process has the potential to produce a wide range of colour tones by varying the proportions of the ferrocyanides in the blend. For example, an image with warm highlights, brown midtones, and blue/black deep shadows would be particularly interesting.
With this motivation, I set out to explore processes for achieving a blend of Prussian Blue and Copper Ferrocyanide. Over the past year, through extensive experimentation, I arrived at several methods to produce blended ferrocyanide prints with varying degrees of complexity and success. In the rest of this note, I will describe the most promising of these processes, which is remarkably simple and has given me satisfactory results. For ease of reference, I will refer to this process as FerroBlend.
Paper
Any paper that works well for Cyanotype should also work well for FerroBlend. I have successfully used Strathmore 300 Bristol 270 gsm, Fabriano Bristol 250 gsm, Brustro Bristol 250 gsm, Magnani 1404 Toscana 300 gsm, Canson Montval Watercolour 300 gsm, Chitrapat 440 gsm Matte, and Chitrapat 440 gsm rough papers. Heavily buffered papers require an acid pre-wash using sulfamic acid or citric acid, followed by a wash in running tap water. Bristol papers should not be given an acid pre-wash as they do not respond well to it.
FerroBlend Sensitizer
To make 2 ml of the sensitizer for brush coating A4-sized paper:
Ammonium chloride is not strictly necessary for papers that have undergone an acid pre-wash. However, it works exceptionally well with Bristol and other papers that do not tolerate multiple wet processing steps. It prevents pigment bleeding and enhances the depth of the darks in the print.
Note: This sensitizer uses significantly more ferricyanide than the classic Cyanotype process. This is intentional and plays a crucial role in the development step.
A two-part concentrate with good storage life can be prepared as follows:
Part A:
Exposure
FerroBlend Developer
To make ~6 ml of the developer for brush developing A4-sized exposed paper:
A long-lasting developer concentrate can be prepared as follows:
Development
Wash
Notes
— Raghu
FerroBlend: A blended ferrocyanide process
Motivation
Cyanotype and Cuprotype are two popular printmaking processes that offer inexpensive and versatile alternatives to silver-based methods. However, both are limited in the range of colour tones they can produce. As the pigment that constitutes the image is a ferrocyanide in both Cyanotype and Cuprotype processes, I became interested in the possibility of a printing process in which the image is formed by a blend of ferrocyanides. Such a process would be interesting to me and many others because the colour tone of the image would be very different from the familiar blue of Cyanotype and the reddish brown of Cuprotype. This process has the potential to produce a wide range of colour tones by varying the proportions of the ferrocyanides in the blend. For example, an image with warm highlights, brown midtones, and blue/black deep shadows would be particularly interesting.
With this motivation, I set out to explore processes for achieving a blend of Prussian Blue and Copper Ferrocyanide. Over the past year, through extensive experimentation, I arrived at several methods to produce blended ferrocyanide prints with varying degrees of complexity and success. In the rest of this note, I will describe the most promising of these processes, which is remarkably simple and has given me satisfactory results. For ease of reference, I will refer to this process as FerroBlend.
Paper
Any paper that works well for Cyanotype should also work well for FerroBlend. I have successfully used Strathmore 300 Bristol 270 gsm, Fabriano Bristol 250 gsm, Brustro Bristol 250 gsm, Magnani 1404 Toscana 300 gsm, Canson Montval Watercolour 300 gsm, Chitrapat 440 gsm Matte, and Chitrapat 440 gsm rough papers. Heavily buffered papers require an acid pre-wash using sulfamic acid or citric acid, followed by a wash in running tap water. Bristol papers should not be given an acid pre-wash as they do not respond well to it.
FerroBlend Sensitizer
To make 2 ml of the sensitizer for brush coating A4-sized paper:
- Water: 1 ml
- Ferric Ammonium Citrate (green): 0.25 g
- Potassium Ferricyanide: 0.2 g
- Ammonium Chloride: 0.25 g (optional)
- Water to make: 2 ml
Ammonium chloride is not strictly necessary for papers that have undergone an acid pre-wash. However, it works exceptionally well with Bristol and other papers that do not tolerate multiple wet processing steps. It prevents pigment bleeding and enhances the depth of the darks in the print.
Note: This sensitizer uses significantly more ferricyanide than the classic Cyanotype process. This is intentional and plays a crucial role in the development step.
A two-part concentrate with good storage life can be prepared as follows:
Part A:
- Water: 60 ml
- Ferric Ammonium Citrate (green): 25 g
- Ammonium Chloride: 25 g (optional)
- Water to make: 100 ml
- Water: 60 ml
- Potassium Ferricyanide: 20 g
- Water to make: 100 ml
Exposure
- 15 minutes using six Philips Actinic BL TL-D 18W lights for a negative with a density range of 1.8–2.2.
- Expose the sensitized and dried paper as you would for Cyanotype (until highlights appear green and deep shadows are reversed).
FerroBlend Developer
To make ~6 ml of the developer for brush developing A4-sized exposed paper:
- Water: 5 ml
- Copper Sulphate: 0.1 g
- Sodium Citrate: 0.4 g
- Surfactant: 1 drop (optional)
A long-lasting developer concentrate can be prepared as follows:
- Water: 60 ml
- Copper Sulphate: 10 g
- Sodium Citrate: 40 g
- Water to make: 100 ml
Development
- Apply half the volume of the developer evenly with a brush.
- Do another pass with the remaining developer.
- Leave the sheet untouched for 5–30 minutes.
- Once the developer is applied, the print starts losing the solarized appearance it had after exposure. It then gains a warmer tone. With some papers, this tone change occurs rapidly (within 5 minutes). With others, it begins after 5 minutes and continues for ~30 minutes.
- Loose pigments (reddish-brown Copper Ferrocyanide) must not form. If they do, it indicates bleeding, which can be remedied by increasing the amount of ammonium chloride in the sensitizer or adding some to the developer.
Wash
- Wash in a tray of tap water containing 2 g of citric acid per liter for 30 seconds to 1 minute with gentle agitation.
- Transfer to a tray of water (pH ~7), face down, and wash for 10 minutes in gently running water.
Notes
- Possible Chemical Mechanism: I am not a chemist and I could be completely wrong about what is happening in the development step. I suspect that, when Prussian White pigments form during exposure, they trap ferrous or ferrocyanide ions underneath or between them. These immobilized ferrous/ferrocyanide ions react with cupric ions in the chelated developer to form Copper Ferrocyanide pigments, which then integrate into the exposed areas, adding a distinct color blend to the print.
- Importance of Excess Ferricyanide: The sensitizer contains an excess of ferricyanide, which is essential for forming Copper Ferrocyanide in the development step. Without this excess, relatively less Copper Ferrocyanide forms during development, resulting in a less warm final print.
- Alternative Sensitizer: Instead of using a sensitizer with excess ferricyanide, you can use a classic Cyanotype sensitizer and compensate by adding ferricyanide in the developer. Just add 0.1 g of ferricyanide for every 0.1 g of Copper Sulphate in the developer solution (or 0.5 ml of Sensitizer Part B per 1 ml of developer concentrate). While this allows the use of commercial Cyanotype sensitisers and shorter scale negatives, it may lead to loose pigment formation and staining with some papers.
- Stain: Some staining can be observed on the papers I tested. This is an area that requires further experimentation and testing, which I have not yet pursued. Unlike in Cuprotype, I am unsure whether a restrainer in the sensitizer will be of much help in this process. I suspect that some of the copper ferrocyanide pigments formed are peptized, though to a significantly lesser degree than in Cyanotype, and that these loose pigments migrate due to repeated brushing, resulting in staining. Perhaps using a puddle pusher and/or a more viscous, slow-acting developer could help mitigate the staining. I need to run tests to confirm.
