system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are the traditional blueprints blue?
gpt
Despite most people using the term Blueprint to mean an original design or plan on how to build something, a Blueprint is actually what it means, a print. A printing of an original design, usually to print a bunch off to give to all the workers that require a copy of the plan. Back before photocopiers, scanners and printers, they had many techniques of duplicating a drawing. One was placing the original drawing (drawn on a translucent layer), on top of another layer with chemicals that when exposed to light would turn another color, that color just so happened to be blue, and leaving the areas covered by the drawing white.