Originally, blueprints were made by exposing light-sensitive paper to sunlight through a translucent sheet of paper or cloth on which the plans were drawn. The areas exposed to light turned dark blue, while the unexposed areas remained white. This resulted in a print with white lines or text on a blue background, hence the term "blueprint". These are also called cyanotypes due to the pigments utilized and were widely used in engineering before being largely replaced by computer-aided design.
