blåprint

A blåprint is a historical type of copy or reproduction of architectural and engineering drawings. The term "blåprint" itself is a misspelling of blueprint, a process that produces a white line on a blue background. These prints were created using a chemical process involving ammonium citrate and potassium ferricyanide, which would react to ultraviolet light. When a drawing was placed on sensitized paper and exposed to light, the areas covered by the drawing remained white, while the exposed areas turned blue.

This method was widely used for its ability to create inexpensive, durable, and accurate reproductions of technical plans. Before the advent of modern digital copying and printing technologies, blåprints were the standard for sharing and documenting designs in fields like construction, manufacturing, and naval architecture. The characteristic blue color and white lines made them easily recognizable. While the term "blåprint" is less common today, the concept of a detailed plan or design remains fundamental to many industries, and the term "blueprint" is often used metaphorically to describe a plan or strategy. The original blue-and-white process has largely been superseded by more efficient and environmentally friendly reproduction methods.