BLUEPRINTS AND COPY MACHINES

Drawings on tracing papers (on vellum or transbonds) are considered to be the original copies.  And after finishing all the drawings be it done manually or by CAD, one usually need a number of copies of these drawings.  CAD drawings though need to be printed usually on large printing machines, some designers want them blue printed.  They like the white or bluelines that go with the copies instead of just the black lines on computer printing machines.