Heliographic copier

In the "argot" of engineers, architects and designers, the resulting plan copies coming from any type of heliographic copier no matter they were either blue or white, were traditionally called blueprints, name derived from the blue background color of the cyanotype technique, which was the previous process for obtaining blueprints, When the diazo based compounds changed the background color to white, in technical environments, -by tradition-, the name for copies of technical drawings remained Blueprint, although in English-speaking countries, it was intended, without much success, to change the name from Blueprint to Whiteprint.

[3] When Herschel developed the process, he considered it mainly as a means of reproducing notes and diagrams, as its use in blueprints.

Introduction of the blueprint process eliminated the high expenses of photolithographic reproduction or of hand-tracing of original drawings.

The different names blue-line copier, whiteprint copier or diazo copier,[9] were given, due to the nature of the process, which consists in exposing to an ultraviolet light a previously sensitized paper with a component called diazo, and finally developing it in a bath (a solution of ammonia in water) which converts the parts not exposed to light, to a dark blue colour (blue-line) over an almost white background.

A little smell of ammonia and a faintly purplish paper colour are the main characteristics of a whiteprint.