cyanotype

In 1842 the British astronomer Sir John Frederick William Herschel developed one of the first methods of producing permanent photographic images. In contrast to the well-known black and white photography, no silver halogens are used, but a solution of iron compounds. A suitable carrier material is required to process the solution, such as watercolor paper, fabrics or solid materials that can absorb the solution. And if the cyanotype is successful, a photogram or photo print in the most beautiful Prussian blue can be seen.

Today's cyanotype is an inexpensive photographic printing process, the character of which can visually compete with old photographic recordings, and all without a darkroom and costly equipment and chemicals. Basically, the typical color scheme is Prussian blue (Berlin blue) and can be tinted brownish to black with tea or coffee and other ingredients. As far as toning is concerned, just experiment to find out other colors and the Internet has various recipes ready.

In the cyanotype, a digital negative is exposed in direct contact to a chemically coated paper or other absorbent carrier using sunlight or UV rays (facial tanner). Then the excess chemistry is washed out (developed) with water and the cyanotopy is ready. But there are still some ways to expand the process to get more results.

What we need!

A lot can be found in the household, but some, such as chemicals, have to be purchased and are available on the web or at the pharmacy.

Chemicals

1. Ammonium iron III citrate (green), solution A

2. Potassium hexacyanoferrate III (red blood liquor salt), solution B

3. Hydrogen peroxide (accelerates oxidation)

4.Distilled water (to prepare solution A & B)

5. Citric acid (slightly acidic water as a developer)

6. If necessary, sodium carbonate (bleach for toning)

7.Tea, coffee, etc. (paint for toning)

8. Transparencies for the inkjet printer

9.Tap water (to wash out the chemicals)

More utensils

11. Fine balance / 1 g accuracy

12. Five photo trays for acidic water (developer), for soaking, oxidizing solution,

Bleaching solution, staining (simple plastic bowls are sufficient)

13. Two wide-neck bottles, brown, 30 ml (for solution A & B)

14. Three disposable syringes, 24 ml (for distilled water, solution A, solution B)

15. A petri dish (solution A & B is mixed in the same ratio)

16. Sponge brush, brush without metal frame, sponge

17. Plastic spoon

18.Clip picture frame (no anodized glass)

19. Facial tanners

20. Disposable gloves, protective goggles and, if necessary, a dust mask

Attention! When handling chemicals, the respective safety instructions and data sheets must be observed in order to protect us and the environment.

Create a digital negative

A basic requirement is that a computer, printer and an appropriate image processing program are available to create a negative.

For successful direct printing, a high-contrast image must be selected and converted into a 16-bit grayscale image. Next, the image is adapted to personal taste, such as contrast enhancement, image sharpening and the desired final size for the contact process. The required print resolution should be at least 300 dpi.

In Photoshop, the image is converted into a negative with the key combination Ctrl + i and mirrored horizontally (Image - Image rotation - Mirror working surface horizontally). The mirroring is necessary because in the contact process we have to place the printing ink of the negative on the emulsion solution of the paper. In order to ensure that the image does not drown during the cyanotype, I recommend using the “ChartThrob” script to be able to create an optimal gradation curve for the image. The photo is then printed out on a suitable transparency film (e.g. for overhead projectors).

The paper

The paper to be used must be able to withstand a lot because of the emulsion solution and sufficient watering (development) and should have a weight of at least 200-300 g / m². Bleached and buffered paper is not recommended because of the chemical substances it contains, as these can react with our solution. It is best to choose watercolor paper made from 100% cotton.

Solution a

consists of 25% ammonium iron III citrate, green and distilled water:

Mix 25 g ammonium iron III citrate, green with 100 ml water or

Mix 2.5 g ammonium iron III citrate, green with 10 ml water

Solution b

consists of 8% potassium hexacyanoferrate and distilled water:

Mix 8 g of potassium hexacyanoferrate with 100 ml of water or

Mix 0.8 g of potassium hexacyanoferrate with 10 ml of water

First, we label the utensils (wide-necked bottles, disposable syringes, plastic spoons) with A & B. This is necessary so that we do not carry the adhering chemicals to each other.

For solution A, we put a small folded sheet of paper on the precision balance and tare it to 0 g. Then we weigh 2.5 g of ammonium iron III citrate and use the paper to sprinkle the ammonium iron III citrate into the wide-necked bottle (A). With the disposable syringe (A) we measure 10 ml of distilled water and carefully inject it into the wide-neck bottle (A) and close it before we shake the bottle so that the ingredients mix. The solution can be stored in a dark place, but it has the property of forming mold.

The same procedure is followed for solution B, except that we mix 0.8 g of potassium hexacyanoferrate with 10 ml of water. This solution should also be kept in a dark place.

Shortly before I want to coat the paper, I mix solution A & B (5 ml A & B each is enough for approx. 3 - 4 DIN A4 sheets) in a Petri dish and gently swirl it. Only now is the solution sensitive to light and the room should be darkened as much as possible.

The Petri dish is big enough to pick up the solution comfortably and in a controlled manner with the brush without applying too much to the paper. Puddles are to be avoided as much as possible, because much does not help much!

Coating and exposure time

The coating with the light-sensitive solution can be applied over the entire surface or we can create a unique piece by creating a creative light-sensitive surface. The solution is applied with a brush without a metal frame or a sponge.

The solution has to dry for some time to be able to penetrate the paper. We can help a little with a hairdryer.

The coated paper must feel dry to the touch (run the back of the hand over the paper) before we can place our negative on it and align it accordingly. Paper and negative are placed in a clip-on picture frame and exposed in the sun or with a facial tanner. The exposure times for my facial tanner are around 3 - 10 minutes. Other factors also play a role here, such as the density of the negative, the UV light source and the distance between the paper and the light source. The selected paper and the composition of the solution also have a significant influence on the exposure times.

In order to find out how long the paper has to be exposed until a satisfactory result is achieved, I will come back to the above-mentioned “ChartThrob” script. I generate 6 gray wedges with the tool and create a series of exposures of 2.5 - 4.5 minutes, which I print out on a transparent film. That means that I expose five of the gray wedges 0.5 minutes longer. After the development and drying time, it can be determined at which exposure time the 255 gray levels from white to black of the respective gray wedge are best represented. If we assume that, for example, an exposure time of 3.5 minutes has achieved the best result, this gray scale is digitized either with a scanner or by taking a photo. The digitized file is called up via the corresponding image processing program without making any changes. In the case of photographed gray wedges, only the white balance of the paper is adjusted. The “ChartThrob” script is called up and analyzes the gray scale and creates an optimal gradation curve for our cyanotype. If all parameters remain unchanged, the generated gradation curve can be used again and again.

Developing and Toning

The exposed image is developed in slightly acidic water (10 g citric acid in 2 l water) for about 1 minute. Immediately afterwards water sufficiently until white paper surfaces appear again and yellow-green to gray chemical residues are no longer visible. Over time you develop the right feeling for sufficient development and watering. Now the picture just needs to dry.

The brilliant blue develops through the oxidation process of the iron citrate during drying. If you can't wait, you can accelerate the process in a water bath in hydrogen peroxide (3.0%). To make a 0.3% solution, 100 ml of hydrogen peroxide are mixed with 1 liter of water. The image should not remain in the accelerating bath for longer than 1 minute and should also be sufficiently watered here so that all chemical residues are washed out of the paper.

Another coloring is also possible by toning, by bleaching the picture in a sodium carbonate solution (30 g to 2 l of water). The blue color that adheres to the iron citrate is washed out and the image gradually disappears until the paper no longer shows any drawings (of course there is no need to bleach that long). After bleaching, sufficient watering is applied to wash the solution from the paper. Then, for example, in tea or coffee, depending on your preferences and personal taste, tone. The color pigments adhere to the iron citrate and slowly the image reappears.

Even after toning, watering is sufficient and the picture can be dried.

It all sounds a bit complex, but it is not and the fun factor is huge and now have fun exploring!

And this is what the end result could look like if everything went well!

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