The blueprint paper recorded the drawing in reverse, black lines appearing white against a cyan background. If you're enjoying this article, consider supporting our award-winning journalism by ...

you’re left with a negative image of white (or whatever color the blueprint paper originally was) against a dark blue background. The technique was faster and more cost-effective than hand ...

you’re left with a negative image of white (or whatever color the blueprint paper originally was) against a dark blue background. You see, the chemicals react and makes the paper blue.