WhatHow
Solution preparation
Paper impregnation
Exposure unit
Test - Line-art mask
Test - Glass negative
Small test
Large test 1
Large test 2
TODO
Cyanotype
is a chemically simple alternative photographic technique.
A substrate (paper, or even cloth or wall) is soaked with a sensitizer solution.
The sensitizer contains a mix of potassium ferricyanide and ammonium ferric citrate.
When subjected to near-ultraviolet radiation, the iron(III) in the ferric citrate oxidizes the citrate,
and gets reduced to iron(II). The Fe2+ ions then react with the ferricyanide and form
water-insoluble Prussian blue.
The remaining soluble ferricyanide and ammonium ferric citrate, still soluble, are then washed out from the substrate with cold water. Substantial effort may have to be spent and some Prussian blue may be washed from the image if the sensitizer didn't soak the substrate sufficiently.
There are many recipes for cyanotype sensitizer. They differe slightly in the ratio of the citrate to ferricyanide, and often significantly in their concentrations. The iron content in the citrate can vary substantially between sources of the chemical, different recipes therefore may be ideal for different people. At least some results should be obtained with any of them.
There are two grades of the citrate - green, with less iron, and brown, with more iron. Different sources suggest either as the better one. Brown one is said to be more sensitive.
See also:
A scaled down recipe, for 10 mL of the solution, was calculated.
1.8 grams of ammonium ferric citrate and 1.0 grams of potassium ferricyanide were weighed, using boats folded from cooking aluminium foil. The thicker, grill-grade, foil was used for its better mechanical properties.
Each batch was then dissolved in 5 mL of water. Ferricyanide dissolved virtually immediately, with great ease. Citrate mostly dissolved easily, but the rest took its time. To accelerate it, the vessel was heated in a beaker of hot water and agitated gently.
 Scale and weighing boats |  Ammonium ferric citrate weighing |  Potassium ferricyanide weighing |  Chemicals prepared for dissolving |
 Chemicals dissolving in 5mL water each |  Hot water bath to help dissolving |  Dissolved chemicals |  Dissolved chemicals |
Pieces of common printer paper, cut from A4 to A5 size, were used as the source material. The two solutions were mixed together. The paper sheets were then brushed with the solution, soaking their top side well, using a folded piece of tissue paper. In retrospect, a piece of foamy sponge or a brush would work better.
Red light was used, to avoid premature exposure of the sensitized papers.
The papers were left to somewhat dry in the darkness, then were placed between sheets of an old newspaper and left to finish drying in darkness, in a closed cabinet.
10 mL of the solution was sufficient for six A5 sheets, and then a little more.
 Ready to mix |  Applying to papers |
A ultraviolet exposure unit with a 5-watt LED
, at 400-405 nm, was used as the source of the
ultraviolet radiation.
A 300-380 nm range source would be preferable.
See also:
A test pattern was drawn with a marker to cover glass, a square of the sensitized paper was then exposed underneath it for about thirty minutes, from about 3 cm distance. The square was then washed in cold water, revealing a well-formed high-contrast blueprint.
 Exposing |  Exposing |  Exposing |  Exposing |
 Exposed |  As-exposed, before washing |  First test, washed |
A somewhat damaged large-area glass negative, dated approximately 1910, was found in the archives. It was used for testing a contact copy with grayscale features.
 Glass negative |  Glass negative |
A roughly 5x5 cm square of sensitized paper was used for the first test. It was exposed with the LED for about 45 minutes, from distance of about 3 cm, through the glass negative. The emulsion was facing the paper, to achieve sharper image.
 Glass negative, small test |  Exposing |  Exposing |  Exposing |
 As exposed |  As exposed |  As exposed |  Washed, still wet |
A larger paper, almost A5, was used for next test. It was exposed for about a hour, from about 8 cm distance.
The glass negative was carefully weighed down, to lay closer to the paper.
After washing, the image was found to be too light, severely underexposed. The washing took more effort this time than with the small samples.
 Paper |  Negative on paper |  Exposure unit |  Exposing |
 Edge, showing shadow of paper |  As exposed |  As exposed |  Washing |
 Dried |  Dried |
A whole A5 paper was used. The exposure time was chosen to be 3 hours, from 8 cm distance. Broken pieces of some other negative were placed in the missing area.
The washing revealed a well-formed image. More exposure could be done, but the image is already satisfying.
 A5 paper |  Negative on paper |  Exposing |  As exposed |
 As exposed |  Being washed |  Being washed |  Being washed |
 Being washed |  Still wet |  Still wet |  Dried |
 Dried | Detail |  Detail |  Detail |