A blueprint is a type of paper-based reproduction usually of a technical drawing documenting an architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan. Etymology The term "blueprint" was originally derived from the visual aspects of prints made using the contact printing process of cyanotype. It is cyanotype which produces the white lines on blue background which are characteristic of the traditional blueprint. History 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 ammonium ferric 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

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