Cyanotype

The cyanotype, also known as a blueprint, iron blue print, is an old photographic process Darkroom typical cyan colors.

History

In 1842, the English scientist and astronomer Sir John Herschel developed this method. The cyanotype was the third method of the daguerreotype and Talbotype / calotype for preparing stable photographic images. It is a method which is based on iron, and not on silver, which is otherwise used in the conventional production of photographic prints ( and the previously invented process ).

Anna Atkins, a British scientist, this photographic technique made ​​famous by their books in which she documented ferns and other plants with cyanotypes. It does this by early application as the first photographer. Artistically, this technique was always something in the corner, it was not counted long time to the photographic precious printing process.

For the reproduction of plans, the cyanotype process was, however, widely used since 1870. The reproduction was even made ​​, and the sensitization of the paper before 1876 in Paris photosensitive papers came into the trade (Marion Co.. ). The exposure was carried out with sunlight. Around 1895 electrical exposure apparatus were introduced. Only in the 1920s were fully automatic machines available who carried out a complete operation ( exposure, development, drying). From the dry -working diazo ( Ozalid ® copy ) the cyanotype was replaced as a method of drawing copy before the Second World War.

Method

Absorbent paper ( (III) ammonium citrate, iron), and potassium ferricyanide and Ammoniumeisenoxalat bathed in solutions of potassium ferricyanide and Ferriammoniumcitrat and then dried. Upon drying, the coating is sensitive to light. Exposure takes place under a shade throwing object as photogram ( object, plant, etc.) or with a negative by UV or sunlight. On an overcast day, the exposure time is daylight 10-20 minutes. In the exposed parts while the iron compound is divalent and insoluble in water - it makes the dye Prussian Blue. The unexposed parts are water soluble and can be developed and wash under running water. The contrast can be increased by bathing in 1% potassium dichromate solution, or by citric acid. The color can be changed by bathing in tannins, oolong tea, cat urine or pyrogallol.

Variants

The original process consisted of the Herschel paper light-sensitive layer of potassium ferricyanide and Ferriammoniumcitrat ( ammonium iron ( III ) citrate ). By Mike goods comes a modern variant of the cyanotype. He used potassium ferricyanide and Ammoniumeisenoxalat instead of Ammoniumeisencitrats. The cyanotype is often confused with the diazo process that was used in architectural offices.