The process I use in my images is called the “Cyanotype Process” and the resulting images are “Cyanotypes”. It originates from the beginnings of photography and was invented by Sir John Herschel, an astronomer and scientist, in 1842. He was just trying to find a way to copy his notes but the process was used one year later already by Anna Atkins in the first photographically illustrated book ever, a book about ferns.
The digital image you want to print needs to be edited and converted into a negative. Then comes the part that is proper handy craft.
The Original, the Negative and the Cyanotype
The cyanotype is exposed by ‘contact printing’: a paper (or fabric) of your choice is coated with an iron salt containing liquid (the sensitiser solution). Surprisingly, this starts light green. It needs to be dried in the dark and ‘matures’ into a slightly darker green. The negative of the image which you want print is then sandwiched onto the coated paper and secured. This bundle is then exposed in the sun.
Initially the image looks very different from what you would expect, but when it is developed in a slightly acidic water bath, it changes slowly. The image needs to be washed and dried and only reaches its final Prussian Blue colour after about 24h.
After drying the print can still be bleached and toned to change the blue to a grey, purple or even brown tone.
This means that there are lots of variables in the process that influence the end product and that no two images will be the same. You will end up with a unique image, printed just like 170 years ago.