The cyanotype process, also known as the blueprint process, was first introduced by John Herschel (1792 – 1871) in 1842. Sir John was an astronomer, trying to find a way of copying his notes.
Botanist Anna Atkins (1799-1871) used the cyanotype process to produce the first book of photographs, Photographs of British Algae: Cyanotype Impressions in October 1843
The cyanotype process was extensively used for copying drawings (blueprints) until the advent of photocopying and digital printing.
The cyanotype process is now used by artists and photographers as an alternate way of producing unique images.
Image by Anna Atkins 1853
How Does The Process Work
Firstly paper or fabric is coated with cyanotype solution containing iron salts and allowed to dry. Objects are then arranged on the paper before clipping it in a glass frame with the objects on the coated side of the paper facing outwards.
The frame is then exposed to ultra-violet light, either from the sun (somewhat unreliable in the UK!) or an artificial UV light source for several minutes.
The paper is then washed or 'developed' in water. Where the objects have prevented the light from striking the paper the iron salts wash away leaving a white image on a bright blues background.
It is possible to make photographs from negatives using the same process described above.
Negatives can be either conventional large format negatives, or digital negatives, made by taking a digital monochrome image, inverting, and flipping it horizontally in Photoshop or Lightroom.
The image is then printed onto special inkjet film and exposed as above. To get a full range of tones, it may be necessary to apply an adjustment curve before printing the negative.