Blueprint: When Plans Were Literally Blue
A *blueprint* is now any detailed plan or strategy, but the word began as a precise technical description: a print that was blue. The distinctive blue-and-white copies that gave the word its name were produced by a photographic process invented not by an engineer, but by an astronomer.
Herschel's Invention
In 1842, Sir John Herschel — one of the most versatile scientists of the 19th century — developed the cyanotype process. Herschel was primarily an astronomer (he catalogued thousands of stars in the southern hemisphere), but he was also a pioneer of photography. He had already coined the terms *photography*, *snapshot*, and *negative*. The cyanotype was one of his many contributions to the new art of capturing images with light.
The process used two chemicals: ferric ammonium citrate and potassium ferricyanide. Paper coated with this mixture and exposed to ultraviolet light turned a deep Prussian blue. Areas shielded from light remained white. The result was a permanent, stable image — white lines on a vivid blue background.
Why Architects Loved It
Engineers and architects adopted cyanotypes because they solved a practical problem: how to make cheap, exact copies of technical drawings. Before blueprints, copies had to be traced by hand — slow, expensive, and prone to error. With the cyanotype process, an original drawing on translucent paper was simply laid over treated paper and exposed to sunlight. The result was a perfect negative copy in minutes, for almost no cost.
The word *blueprint* first appeared in print in 1886. Within two decades it was standard terminology in architecture and engineering.
The Figurative Leap
By the early 20th century, *blueprint* had escaped the drafting room. Politicians spoke of "blueprints for reform." Business leaders presented "blueprints for growth." The metaphor worked because blueprints implied precision, forethought, and technical competence. Today, few people have seen an actual cyanotype, but the word remains the default metaphor for any detailed plan.
Anna Atkins
One of the first creative users of cyanotypes was not an architect but a botanist. Anna Atkins used Herschel's process to create exquisite prints of algae and fern specimens, publishing them in 1843 — making her work arguably the first book illustrated with photographic images.