(or Blue Print)
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In June 1842, Herschel read a paper to Royal Society on the effect of light on vegetable pigments, particularly the use of the pigment in geranium flowers, for photographic purposes. It was a rotten summer and the exposures took days. As an afterthought he noted the effect of light on certain iron salts which were “reduced to the metallic state” by light, this means that the metallic salt was changed back to iron, and that other metallic salts associated with the iron salts would be “reduced” in the same way to produce photographs; two iron salts produced a cyanotype, an iron salt with a gold salt, a chrysotype. Herschel also noted the effect on silver salts which was later became the kallitype. In 1843 Anna Atkins produced her book on British algae, illustrated with cyanotype photograms, which was the first book with a body of photographic illustrations.
The wonder of the cyanotype is that although it is safe, cheap and very simple to produce, cyanotype prints are stable, permanent, and have beautifully subtle gradation across a wide tonal range.
Even the disadvantage that they are blue can be changed with toning which can produce interesting and sometimes beautiful results.
A straight cyanotype
Water quality can change the colour of a Cyanotype.
A cyanotype toned in ammonia and tannic acid
with a superimposed straight cyanotype print.
A cyanotype toned in tannic acid
and sodium carbonate.
A cyanotype “painted” with pastels
At Hands-On pictures we have managed to develope a method of making cyanotypes that is still cheap and simple but allows exposures which are far shorter. The system also gives images of a beautiful blue black which tone and split tone well. The process grew out of our work on the chrysotype.
We have called these methods the cyanotype rex and chrysotype rex.
A cyanotype rex - Wells Cathedral
Chemically a cyanotype is achieved when light reduces an iron salt ferric ammonium citrate, from its ferric to its ferrous state. The result is a negative image. But if a ferrous salt, potassium ferrocyanide (note the “o”) is used to “develop” an image resulting from exposing a ferric salt to light, the result is a positive image.
Cyanotype kits for kids can be bought at museum shops. I have made cyanotypes with classes of six year olds who were thrilled at this introduction to photography and making things for themselves. This is an indication of how easy and safe the process is. The main iron salt, ferric ammonium citrate, is used as a food additive while the other, potassium ferricyanide (note the “i”), sounds nasty but is only likely to cause trouble if it is mixed with strong acids.
A Cyanotype on calico
PAPER, TEXTILES AND OTHER SURFACES
Most mat papers will accept cyanotypes as will natural fibers in textiles. It is advisable to size paper with a 2 % gelatine size before applying the cyanotype mixture. It is also a good idea to wash the dressing out of textiles using soap flakes. Do not to use washing soda as it will “tone” the cyanotype.
A cyanotype over a brown gum print
Water at 20°C 100ml
Ferric ammonium citrate (green) 20g
(this is a food additive used in the production of “Irn Bru”, iron tonics and corn flakes)
Water at 20°C 100ml
Potassium ferricyanide 8g
Dissolve, then mix the two solutions. Store in brown bottle in the dark. If the two solutions are kept separately some claim that they will keep longer. This may be true after a year or so, but in practical terms it is a matter of preference. This really is a dollop of this and a dollop of that recipe.
- Coat the (sized) paper or textile with the two solutions mixed in equal proportions in subdued light using a hake brush, (a Chinese goats hair brush) reserved for the purpose.
- Dry in the dark
- Expose under a negative with a density range of about 1.4 , (somewhat denser than a silver gelatine negative intended for printing onto silver gelatine paper), until all shadow tones have reversed and all other tones that are intended to show in the final print are dark blue. Get the negative right and the exposure right!
- Develop by washing in tap water until the picture looks right. If the negative has insufficient density range or is exposed only until it only looks like as the final image should, everything but the deepest shadows will wash off during development or, if pulled early from the development wash, will run or leave yellow iron stains.
- Hang up to dry.
- Some suggest adding hydrogen peroxide to the wash water to oxidise the print to a dark blue but this will happen naturally as the print dries.
Once the print has arrived at the reversed stage during the exposure, if you then double that exposure and then develop the print in a dribble of water overnight, the print will no longer consist of blue ferroprussiate but will be pink iron hydroxide. This produces a very interesting final result when the cyanotype is then coated with coloured gum bichromate and re-exposed and developed.
If you want a sharp image you should use thin flat objects. It is better to hold them in place between two sheets of glass. If the object is opaque, the result will be a white “shadow” surrounded by blue. If the object has translucent areas these will be reflected in the print.
A Toned Cyanotype Photogram
A photogram of rose branch
There a number of ways of toning cyanotypes but the two detailed here are the simplest and enable a range of tones and colours.
It is worth remembering:
- that the results are not necessarily permanent but may well be for all practical purposes
- that the amounts of the toning chemicals are small
- that as time in the toner, temperature and strength of the solutions all affect the final colour, or proportion of split toning, it is best to record a particular method if you want to repeat it (split toning is where you take the print out of the toner before all the colour has changed)
This method uses tannic acid to slow the action of the toner, sodium carbonate (washing soda).
Solution ONE , 1 g of tannic acid in 100ml of water
Solution TWO 1 g of sodium carbonate in 100 ml of water.
Immerse the developed cyanotype in solution ONE for a few seconds and then wash, retaining the tannic acid for future use. Immerse the cyanotype in solution TWO until the desired effect is achieved.
This should produce a brown cyanotype. Wash for five munutes.
Solution ONE, 5 ml of household ammonia in 100ml of water
Solution TWO, 1g of tannic acid in 100 ml of water
Immerse the washed and developed cyanotype in solution ONE; the effect will be to bleach the print. The extent of the bleaching will affect the extent of the split toning. Wash the print, retaining the ammonia solution for future use, and then immerse it in solution TWO until the desired effect is achieved.
Wash for five minutes.
(A weak solution of tea can be substituted for the tannic acid).
POSITIVE CYANOTYPE - Pellet’s process
5 g oxalic acid
10 ml ferric chloride (45 Baume)
9.5 g gum Arabic
100 ml water,
Mix into a solution and coat the paper.
Expose for five minutes in sunlight or 15 minutes or so under a UV lamp until the a pale yellow image can be seen
Develop by brushing on a 20% solution of potassium ferrOcyanide.
Place in a dish of clean water for some minutes.
Transfer the print to a dish of 1% hydrochloric acid until the whites clear.
This process is intended for line images but continuous tone images can be achieved - although there are far easier ways of doing it !
Note : Ferric Chloride is used for etching gravure plates