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Sir John Herschel

natural philosopher, astronomer and inventor of the cyanotype process

Site of the twenty feet reflector at Cape of Good Hope Sept. 1834

Early nineteenth century England


John Herschel by Julia Margaret Cameron

Here i will expand on the close circles of early nineteenth century England. I want to explore the relationship between Thomas Wedgwood (pioneer photographer), Charles Darwin (biologist, who married Wedgwood's cousin) and finally John Herschel (inventor of the cyanotype process, who met Darwin in Cape Town during the famous voyage of the Beagle). Since my interests lie in photography and biology (mainly the life and work of Charles Darwin), I will keep to this close circle.

Starting with Thomas Wedgwood, son of the potter Josiah Wedgwood, who pioneered in photography from a early as 1795. Thomas Wedgwood was also Emma Wedgwood's uncle who married Charles Darwin on 29 January 1839. Charles Darwin would later meet

Sir John Herschel in Cape Town in 1836.

to be continued...


Charles Darwin by Julia Margaret Cameron

Cyanotype process

In principle, the cyanotype is a photographic printing process. It produces a cyan-blue print, also referred to as Prussian blue or Berlin blue. For a long time this process has been used by engineers to produce copies of drawings, known as blueprints. 

The process uses two chemicals:

Ammonium ferric citrate, (NH4)5[Fe(C6H4O7)2]

Potassium ferricyanide, K3[Fe(CN)6]

To create light sensitive paper (photographic paper) using these chemicals, you first need to make two solutions. For a general mixture one can use the following solutions:

  • 30g Ammonium ferric citrate

  • 100ml water


  • 10g Potassium ferricyanide

  • 100ml water

Once the chemicals are dissolved in the water, the two solutions can be mixed 1:1 to create a mildly photosensitive solution. The solution can then be applied to receptive surfaces, such as watercolour paper or textile. Once applied, the solution needs to dry (preferably in the dark) in order to become sensitive to UV (ultraviolet) light. When the solution is cured you have photographic paper.

To create an image the paper needs to be exposed to the sun or an artificial uv light source for several minutes, depending on the amount of UV light. For example, ten minutes in direct sunlight should be long enough to harden the chemicals. While a cloudy day will not affect your prepared materials. After exposure, the photograph needs to be rinsed in water for ten to fifteen minutes. During this time your image will appear and all the excess chemicals will rinse out. When not rinsed properly, there is chance remaining chemicals will continue to darken your image, eventually turning it completely blue.

Experiments with the cyanotype

Unfixed cyanotype in the sun, the image slowly fades


Nitophyllum stellato-corticatum,
three different exposure times


Ceramium deslongchampsii,
three different exposure times

cyanotype exposure times

experimentation with different chemical mixtures and exposure times, each strip represents 1 minute of exposure. The more water was added to the solution the sooner  a blue tone would appear. Also interesting to note, is that there is little difference between the 4 and 9 minutes of exposure. After 10 minutes the blue appear 'burnt'.

Cyanotype process
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