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Cyanotype prints
In the contact printing method of cyanotype the paper is sensitized with one part green ammonium iron(III) citrate
(18 g/100 ml) solution and one part potessium hexa cyano ferrate (III) solution (10 g/100 ml). The first solution is the same
as the one in the van Dyke method (Kallitype printing). During the exposure to UV light
the iron(III) in the ammonium iron(III) citrate is reduced and react with the potessium hexa cyano ferrate (III)
to produce a precipitate of the so called Berlin blue compound KFeIIFeIII(CN)6.
The contact printing under UV light is fairly slow and can be running up to 30-60 minutes.
The print is developed in water and becomes darker blue when drying. The dark color of the print can
be enhanced by adding 3% hydrogenperoxide to the developer. The blue color can become somewhat weak by
the time but can be re-enhanced by oxidation again. This so called blue print is most likely the most permanent
printing method known and excellent prints from before 1850 are known.
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