Blueprint Symbols: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. Invented 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.
The encyclopaedia of practical carpentry and joinery : comprising the choice, preservation, and strength of materials, explanations of the theory and practical details, a complete system of lines for the carpenter, joiner, & staircase builder, together with an account of the improvements effected in England and on the continent, and illustrations of the most remarkable executed works : Tarbuck, Edward Lance, editor : Free Download, Borrow, and Streaming : Internet Archive