Cyanotype printing is a method of image making on light sensitive paper. Unlike most photo sensitive techniques it utilises iron rather than silver based salts. It is characterised by the blue and white prints that it produces,(known as “blueprints” when used to reproduce technical drawings).
The process was invented by Sir John Herschel in 1842. His invention was initially principly taken up by botanists for the purposes of plant specimen illustration, notably Anna Atkins. Following Herschel’s death in 1871 the process was “reinvented’ and used principally as a reprographic system particularly for technical drawings up until the 1950’s. Interest in cyanotype as a photographic printing medium has grown again since the 1970’s to the present day.
Exposure times are relatively slow and the chemicals require exposure to light in the ultra violet spectrum. The long exposure times and high light levels required mean that it isn’t considered suitable for use in cameras but is instead primarily used for contact prints from negatives or direct from objects placed on the paper (photograms). Strong sunlight is an ideal light source but UV bulbs can be used as an alternative.
Preparing the photosensitive solution
The exact recipes for the photosensitive solution have varied in some respects over time. The following is a typical 20th century recipe. Precaution:Use disposable gloves and a face mask whilst handling the powdered chemicals.
Add 25g of Ferric Ammonium Citrate to 100ml of water in a glass container
Add 10g of Potassium Ferricyanide to 100ml of water in a second glass container
The chemicals dissolve readily in cold water and are not light sensitive until they are mixed together. You will need some small electronic scales to measure the chemical quantities.
(Chemicals can be purchased from Silverpoint ( http://shop.silverprint.co.uk/Cyanotype/products/541/ )
Coating your paper
You will then need to move into a photographic darkroom with a safelight or a darkened room with very low level tungsten lighting. Add each of the solutions into a third container. To enable storage of the liquid its best to use a dark brown glass jar with a light tight lid. Stir briefly to ensure both solutions have mixed together.
Now use a brush to apply the light sensitive solution to your paper. A foam brush works well. Then return any unused liquid to the dark brown storage jar and set aside your paper to dry in full darkness.( NB For longevity of the Cyanotype print its best to use a “non buffered” paper i.e. one that hasn’t had chalk/calcium carbonate added to increase its alkalinity)
Once dry keep the paper in a light tight black plastic bag or a light tight cardboard roll until required for use.
Exposure to direct Sunlight
On a bright sunny day prepare the objects, masks or drawings on acetate/tracing paper that you want to use to create your image and get a clock or watch to hand so that you can keep an eye on the exposure time.
Remove the paper from the roll spread out in direct sunlight with the pale yellow side uppermost. Immediately work quickly placing your objects on the paper. Items placed immediately will leave white marks. Items placed later will leave marks which are very pale blue progressively getting deeper, the later that they are placed. Areas left in full sun will be a deep blue with 3 minutes exposure to the brightest UK sunshine.
When 3 minutes is up quickly move the objects aside and put the paper back in its black plastic bag or light tight cardboard roll.
( Its useful to have created several long strips of cyanotype paper that you can use as exposure test strips , use some dark card and reveal more of the strip each 15 or 30 seconds in order to get an accurate idea of exposure times for your particular lighting conditions)
Exposure using UV Lamp
In the absence of strong sunlight its possible to use a UV floodlight to expose cyanotype. Exposure times are longer than with sunlight. A 40W LED UV floodlight mounted about 2 feet above a worktop will expose cyanotype paper in about 10 to 15 minutes.
If your work room is lit with subdued daylight then the advantage of using the UV floodlight is that you can spend much longer composing the items that you are placing on the cyanotype paper before you switch the UV lamp on and start the exposure. Its still best to store the cyanotype in a light tight container or envelope when you are not using it to ensure that it isn’t degraded.
( If you make a UV lamp exposure strip then try using minute intervals between 10 and 15 minutes as a starting point )
In subdued light conditions take the exposed cyanotype out of its light proof container and immediately immerse in a tray of cold water. agitate gently for several minutes. The cyanotype will reveal its characteristic cyan colouring and the water will colour slightly. Change the water for a final rinse of another couple of minutes allow excess water to drain off then place the print between two sheets of blotting paper and place under a weighted plywood board and allow to dry flat over a day or so. ( NB longevity of Cyanotype prints is increased with thorough rinsing but this should be balanced against dispersion of the blue colouring that may occur with rinsing)
Longevity of Cyanotype prints
Cyanotype prints made by Anna Atkins in the 1840s are still in existence. However some care is required for their longevity. To minimise fading of the image take note of the following:
- Avoid permanent display in daylight (returning prints to darkness can reverse some colour loss)
- Rinse we’ll during processing to reduce presence of any remaining photosensitive solution or other impurities.
- Avoid use of buffered papers ( i.e. papers incorporating chalk or calcium carbonate)
- Do not over agitate or use fast running water during rinsing to minimise dispersal of the blue colour
- The chemicals used in cyanotypes, and the use of non buffered ( i.e. neutral or slightly acidic) paper can result in brittleness of the paper substrate over time.