Cyanotype is a process of creating as print using a chemical process and ultra-violet light. The usual final print is normally a cyan blue, hence the name. It is possibly best known from the 20thcentury process of creating engineering drawings known as ‘blueprints’.
To start the process, two chemicals are required, ferric ammonium citrate and potassium ferricyanide. Both chemicals are fairly harmless, although with any chemicals it is best practice to wear gloves, safety glasses and a mask, especially if asthmatic. Keep the potassium ferricyanide away from anything acidic, otherwise toxic cyanide gas could result.
Although ready-made cyanotype liquid can be purchased, it is much cheaper to get the individual chemicals and make it onsite.
The process involves multiples of 10g of potassium ferricyanide and 25g of ferric ammonium citrate. Put the chemicals into two separate containers and add 100ml of water to each, and stir well. Once well mixed, combine the liquids. The resulting liquid can be kept in a sealed container for a number of weeks before it deteriorates.
the resulting liquid is a green colour, nothing like the cyanotype prints that will result. Paint the liquid onto the preferred media. This can be heavy paper, such as watercolour paper around 200gms, fabric (natural is preferable as it is absorbent) etc. If using something like clay remember it cannot be fired for two reasons. One is the kiln process will release cyanide, and the other is that the heat will react with the cyanotype, giving a totally different finish.
Next is deciding what to use to create the final print. Objects can be used, such as feathers, leaves, flowers etc. the choices are inexhaustible, however for best results using thin objects work best.
Photographs can also be used, using Photoshop to create a negative. The process is relatively simple. Select the image in Bridge, and open in Camera Raw. Open Adjustments, 4thicon from the left below the histogram, and convert to greyscale.
With a Mac, open the image, select mode and grayscale. With the curves icon, push the left of the line to the top left corner, and drag the right to the bottom. This will create a negative.
It is now ready to print. Select layout, and scale to fit media type. Use a transparency sheet to print on.
Taking the prepared media, place the object/negative on it, and expose to ultraviolet light. This can be sunlight, or an ultraviolet light source. The process takes around 10-20 minutes depending on the light source strength.
The ultraviolet light and the citrate convert the ferric (iron III) to ferrous (iron II) which then reacts with the ferricyanide to give a resultant Prussian blue colour, which when washed with water gives the final fixed image.