Heliographic copier
A heliographic copier or heliographic duplicator is an apparatus used in the world of reprography for making contact prints on paper from original drawings made with that purpose on tracing paper, parchment paper or any other transparent or translucent material using different procedures. In general terms some type of heliographic copier is used for making: Hectographic prints, Ferrogallic prints, Gel-lithographs or Silver halide prints. All of them, until a certain size, can be achieved using a contact printer with an appropriate lamp (ultraviolet, etc...) but for big engineering and architectural plans, the heliographic copiers used with the cyanotype and the diazotype technologies, are of the roller type, which makes them completely different from contact printers. 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. Depending on the color or the line and background, the appropriate paper may be developed for blueprints (blue background), whiteprints (blue line and white background), black line (white background) and sepia, using the same machine and process. Using the right compound some "cyano copiers" could be adapted to be used as "diazo copiers". (Wikipedia).
