A
blueprint is a reproduction of a
technical drawing, documenting an
architecture or an
engineering design, using a
contact print process on light-sensitive sheets. Introduced in the 19th century, the process allowed rapid and accurate reproduction of documents used in construction and industry. The blue-print process was characterized by light colored lines on a blue background, a
negative of the original. The process was unable to reproduce color or shades of grey. Various base materials have been used for blueprints. Paper was a common choice; for more durable prints
linen was sometimes used, but with time, the linen prints would shrink slightly. To combat this problem, printing on imitation vellum and, later, polyester film (
Mylar) was implemented.