Cyanotype

One of the first photographic processes to use a negative was the cyanotype (also called sun-prints).

The cyanotype uses an iron-based chemistry in which a mixture of ammonium ferric citrate and potassium ferricyanide dissolved in water is used as the sensitiser.

The solution is painted onto pre-shrunk watercolour paper and dried in the dark - producing a pale yellow coating on the paper.  The paper is then placed in contact with a negative and sandwiched in a printing frame with a clear glass window.  The paper is then exposed to ultraviolet light for several minutes until the coating 'bronzes'.  When the paper is washed in cold running water, the exposed areas are rendered blue (by the Prussian blue pigment produced by the action of the light on the sensitiser).

For this process, I again used the ChartThrob (http://www.botzilla.com/blog/archives/000544.html) program to calibrate the negative.  The next step with this image is to attempt to put two layers of gum over the image to duotone the highlights and shadows.  More later (when it works???)