Blueprint is a word whose literal meaning—a blue print—describes a specific 19th-century photographic process, while its figurative meaning—a detailed plan or model—has become so dominant that most speakers have no idea the word ever referred to anything actually blue.
The compound combines blue (from Old English blǣw, from Proto-Germanic *blēwaz) and print (from Old French preinte, from Latin premere, to press). The compound was created to describe the output of a specific technical process: the cyanotype, invented by the British astronomer and chemist Sir John Herschel in 1842.
Herschel developed the cyanotype as a simple, inexpensive method of reproducing documents and drawings. The process involves coating paper with a solution of iron compounds (ferric ammonium citrate and potassium ferricyanide), placing a translucent original on top, and exposing the assembly to sunlight. Where light reaches the paper, the iron compounds react to form Prussian blue (ferric ferrocyanide), a deep blue pigment. Where the original's lines block the light, the paper remains white. The result is a
One of the first and most creative users of the cyanotype process was Anna Atkins, a British botanist who used it to create detailed images of algae, ferns, and other plant specimens. Her work, Photographs of British Algae: Cyanotype Impressions (begun in 1843), is considered the first book illustrated with photographic images and makes Atkins one of the pioneers of photography.
The cyanotype process proved ideal for reproducing architectural and engineering drawings. The ability to create accurate copies of large-format technical drawings cheaply and quickly made blueprints standard in architecture, engineering, and construction by the late 19th century. The word blueprint, first attested in 1886, quickly became synonymous with technical drawings of any kind.
The metaphorical extension from a specific type of drawing to any detailed plan occurred naturally and rapidly. By the early 20th century, blueprint was being used figuratively: a blueprint for success, a blueprint for reform, a blueprint for the future. The metaphor works because a blueprint is not the thing itself but a detailed guide for creating the thing—it specifies every dimension, material, and relationship.
Modern technical drawing has largely abandoned the cyanotype process. Computer-aided design (CAD) systems produce digital drawings that can be printed on any paper in any color. The distinctive blue-and-white originals have almost entirely disappeared from professional practice. Yet the word blueprint persists, its figurative meaning now entirely independent of its literal origin.
The word has been translated or calqued into several languages. German Blaupause (blue trace) and similar formations in other languages reflect the original process, while the figurative meaning of detailed plan has been borrowed along with the word itself.
Blueprint belongs to a category of words whose metaphorical meanings have completely overshadowed their literal origins. Like deadline (originally a line around a Civil War prison that prisoners would be shot for crossing) and red tape (originally the red ribbon used to bind legal documents), blueprint has transcended its specific origin to become a universal term in the language of planning and design.