The cyanotype process was devised and described by the astronomer, Sir John Herschel in 1842.  Herschel was a friend of Fox Talbot, the father of modern photography, and had conducted many experiments with light sensitive materials.  However, Herschel’s motives were entirely scientific and he posed no commercial threat to Talbot.

            The cyanotype process is cheap, safe, and is a good way of introducing children to photography and the physics of light.  It needs only two chemicals, and is as permanent as the support it is printed on.  It is developed and fixed in plain, running water.

            It is a contact print process so the main disadvantage is obtaining large enough negatives.  I use a 5x4 film camera and contact print from the negatives it produces.  If you have a 35mm or medium format camera, you will need to scan, or get scanned, the negatives to print out large negatives on overhead projection film (OHP).  If you have a digital camera, the chances are you already have image editing software on your computer to create negatives with OHP film.

            To make the light sensitive emulsion, take 10g of ferric ammonium citrate, the green form, not brown, which is useless for this purpose, and mix in 50 ml of tap water, pour into a 100ml brown bottle, available from chemists.  Then mix 4g of potassium ferricyanide (note, ferri, not ferro), mix with 50ml of tap water and pour into another brown bottle.

            This can all be carried out under normal room lighting, curtains closed during daylight hours.

Remember the safety precautions with chemicals, rubber gloves, goggles, don’t get chemicals in your mouth, wash your hands, don’t work on food preparation surfaces; most importantly, supervise children.

            To coat the paper, mix equal amounts from the two bottles in a saucer and brush on to your paper.  Cheap drawing paper will do as long as it is strong enough to be soaked.  I use Saunders Waterford 140 lb watercolour paper, hot pressed or NOT (cold pressed) surface.

            Dry the emulsion off with a hair dryer and tape to it, along one edge, your negative, sandwich this between a piece of hardboard and a sheet of glass, fixing with bulldog clips.  Put in the sun, or in front of a UV light source and check by unclipping and lifting your negative, say, every five minutes, when the print looks right it will still need longer, until the shadows take on a metallic grey look.

            Wash/develop the print under running water for about five minutes then hang up to dry, it will take about a day for the full colour to become apparent.

            Have fun.