Cyanotype is an iron-based process. It is one of the oldest processes used for making prints and is the basis for the process used to make document copies called “blue-prints”.

 

Invented/discovered by John Herschel in 1840 as means of copying his notes, this process uses iron compounds that react to light. These iron compounds are much less expensive than the much more light-sensitive silver salts that replaced them in later photographic printing technologies.

 

Cyanotype Formula

In my use of the cyanotype process, strong, watercolour paper is coated with a mixture of two solutions:

Solution A is 25 grams Ferric ammonium citrate (green) and 100 ml. distilled water

Solution B is 10 grams Potassium ferricyanide and 100 ml. distilled water

Sometimes with a few grammes of Oxalic acid.

 

In dim lighting (not fluorescent) I use a soft Hake brush to apply the liquid and then leave the paper to dry naturally.

The paper is best used fresh, but I have achieved some good results with paper that has been dark-stored for several months.

 

I place a negative onto the cyanotype paper in a contact printing frame/press.

Negatives with a good tonal range work best. 

 

I use the sun if the weather is good, to expose the paper - anything from 5 to 30 minutes depending on the time of year/day/cloudiness and density of the film negative.

 

One to two hours can be needed for a paper negative but the results are equally as good as that from the film negatives.

 

I have a 30Watt LED UV lamp if the sun isn’t available, or if I want to a controlled environment for reproducing images with greater consistency.

 

Using a contact printing frame allows me to inspect the progress of the exposure. I am looking for the image to be mostly blue with the lightest part of the negative rendered as areas of grey and the blackest areas rendered as yellow. Too little exposure and the image seen on the paper will wash away during development. 

 

Development is achieved by washing in slightly acidic water. In my home area the water is alkaline so I wash the print in 1% citric acid, until all the yellow on the front has gone. 

 

At this point the print needs to be left to oxidise and darken. However, for the impatient - a wash with dilute Hydrogen Peroxide achieves the same effect.

 

Once washed from the peroxide, I can see what further treatments could enhance the print.

A rinse, to a soaking, in alkaline washing soda will darken the blues, add a bit of purple and then eventually bleach the blues to yellow.

 

After  the chosen rinse/soak treatment, further toning of the image can be done with solutions that contain tannins - Tea, Coffee, Wine, Oak bark liquor.

 

Colours ranging from browns to greens to blacks and pinks can be achieved with different solutions. 

 

On glass

All of the previously described cyanotype processes can be applied to a layer of cyanotype gelatine on glass.

 

I dissolve 20g of gelatine in 200ml cyanotype solution. Once made the jelly that results is stored in a black plastic bag in my refrigerator.  

 

To apply this to glass I warm the gelatine in water (I use an old slow-cooker) and then, with a syringe take 3 ml or so to squirt gently onto the glass. Once coated (collodion style) I stand the plate up in a rack to drain. This does result in some unevenness - but this is better than having too thick a layer of gelatine on the plate.

 

The plate is then exposed and developed as with paper.