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Cyanotype - Historical Context:

Cyanotypes or Blue Prints or ferro prussiate Prints were invented by Sir John Herschel in 1842. This is one of the earliest photographic processes, and also one of the easiest and most practical.

Blue Prints

Until recently, it had been widely used by engineers and architects to reproduce technical drawings and was known as blue prints. An original drawing made on tracing paper with black ink, which might be the plans for a building, was laid, onto a sensitized sheet, contact printed and then developed.The blue print gained the name because the background developed blue, and the fine lines of the plan as white lines. This enabled several plans to be issued to various tradesmen for use with their aspect of the construction. I remember my father making them for the installation of fire alarms. The term Blue print became synonymous with plan, and is sometimes still used today.

Suitable paper is brushed with a solution of ammonio-citrate of iron and potassium ferricyanide. It was dried in the dark and exposed by contact printing in daylight, which produced a week green image. The print was then washed, which served simultaneously to remove the coating unaffected by light and to reduce the remaining salts, forming the image to an insoluble Prussian blue. The image is permanent, and no chemical fixing was necessary. When white paper was used, the image appeared bright blue on a white ground. Cyanotypes can be toned by chemical means to various other colours, but this is often unpredictable and sometimes affects their stability. The process itself is very fine, the image appearing matt and slightly embedded in the paper, as with any salt print. It has been used infrequently by photographers to print camera images undoubtedly because of its extraordinary and surprising colour.

A very early use of the cyanotype as a practical means of making a permanent record was the work of Anna Atkins, who made photograms of seaweed by this method to illustrate a privately published book in 1843. She also produced the text by this method. There was a later vogue for this process around the of the century, when several photographers used it, including Frances Benjamin Johnston, Charles Lummis, Edward Curtis, as well as many amateurs in America.

A commercial Cyanotype kit

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