(page under construction)
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
to
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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
