@louhikarme there is also the little issue that what we get are usually not the actual blueprints (I mean the technical drawings) like the ones they use to manufacture something.
Anyway, a blueprint is just a copy of a drawing, so any drawing could be made in a blueprint. The naming is not incorrect, it just sounds more ‘official’ than it is.
They make a drawing on transparent paper and then lay that on top of special paper with a light sensitive layer (which is yellow, by the way), shine a bright light over it so only where the lines are on the drawing the yellow layer stays. and then they fixate those lines with ammonia, which turns them blue. Hence the name;)
