White on Blue

Blueprints are a key feature in the field of architecture. They are the actual visual for the design of a building that tells opthers how to build the building properly. A blueprint is a type of paper-based reproduction usually of a technical drawing, documenting an architecture or an engineering design. The blueprint process is essentially the cyanotype process developed by the British astronomer and photographer Sir John Herschel in 1842. The photosensitive compound, a solution of ferric ammonium citrate and potassium ferricyanide, is coated onto paper. Areas of the compound exposed to strong light are converted to insoluble blue ferric ferrocyanide, or Prussian blue. The soluble chemicals are washed off with water leaving a light-stable print.