A blueprint is a reproduction of a technical drawing using a contact print process on light-sensitive sheets. Introduced by Sir John Herschel in 1842,the process allowed rapid, and accurate, production of an unlimited number of copies. It was widely used for over a century for the reproduction of specification drawings used in construction and industry. The blueprint process was characterised by white lines on a blue background, a negative of the original. The process was not able to reproduce color or shades of grey.