most economic methods to reproduce large engineering and architectural drawings. Fading prints A quirk of diazo blueline prints is that with continued exposure to ultraviolet light, either from natural sunlight or from typical office fluorescent lighting, a blueline copy can fade over a span of months (indoors) or just days (outdoors), becoming illegible. This fading process thus requires reduplication of the original documents every few months in a typical office for any project using bluelines. Hence, blueline drawings that are used as engineering working copy prints have to be protected when not in use by storing them in flat files in the dark. Incandescent lighting was often used in areas where blueline engineering prints needed to be posted on a wall for long periods to hinder rapid fading. Improperly exposed bluelines are more likely to fade at an increased rate since the chemical reaction in the ammonia phase continues until the process is completed. But also properly exposed bluelines should not be exposed to the elements, and bluelines kept in flat files or hanging on racks in a cool, dry room often retain the majority of their lines and are able to be subsequently scanned into a digital format for various purposes. Demise of the technology The blueline print process was largely abandoned within the architectural/engineering community around the early 2000s. Contributing factors were the development of computer aided drafting and printing, the speed of machine printing, and the introduction of larger xerographic machines or large format printers from companies like Ricoh and Xerox. The cost of blueline production materials and equipment, the fact that the prints themselves faded in sunlight, and the need to use the pungent chemical ammonia as a developer sped up its replacement. See also Azo compound Blueprint Heliographic copier Ozalid References Non-impact printing Technical drawing Infographics