blueprints

Blueprints are reproductions of technical drawings used to convey design information in fields such as architecture, engineering, construction, and manufacturing. Traditionally, a blueprint displayed white lines and text on a blue background, showing plans, sections, elevations, and specifications.

The term and method originate from a 19th-century process developed by Sir John Herschel in 1842 called cyanotype. It uses iron salts, such as ferric ammonium citrate and potassium ferricyanide, to produce a light-sensitive surface. When a drawing on translucent paper is placed in contact with this surface and exposed to light, the unexposed areas wash away to reveal a white line image against a Prussian-blue background. The result was inexpensive, durable, and easy to reproduce many copies of a drawing.

In practice, blueprints functioned as the practical medium for distributing construction documents. The characteristic white lines denote structural elements, dimensions, notes, and symbols, allowing builders and manufacturers to interpret the design accurately. The process favored rapid reproduction and straightforward copying, which facilitated collaboration across teams and sites.

With the rise of photographic reproduction and digital technologies, the term blueprint has persisted as a general label for technical drawings, even when not produced by the cyanotype method. Modern workflows typically rely on digital CAD models and printed or electronic drawings, such as PDFs, while the color blue may be replaced by black-on-white or other formats. Nevertheless, the blueprint remains a historical cornerstone of architectural and engineering communication.