Not so many years ago copies (of technical drawings), so called blueprints (actually whiteprints): https://en.wikipedia.org/wiki/Whiteprint https://en.wikiped

Not so many years ago copies (of technical drawings), so called blueprints (actually whiteprints): https://en.wikipedia.org/wiki/Whiteprint https://en.wikipedia.org/wiki/Whiteprint were made from transparent originals using UV lamps on paper that developed through being exposed to ammonia vapours. Any architect/engineer would have (instead of a plotter) one of these machines, with a transparent glass or perspex/lexan pipe with inside one, two or three UV "neon" tubes in which you fed the transparent coupled with the reactive paper, a motor and a large belt would make the paper travel some 270 ° around the UV illuminated pipe, thus impressing the paper. Higher end machines had an internal "developing station" (basically a perforated pipe inside which small quantities (drops) of ammonia were slowly pumped and around which only the UV impressed paper passed), and there was a fan extracting air to a vent pipe leading outside. The earlier and lower end machines had a separate "developing station" consisting in a box (more sort of a large pipe) with a container of ammonia on top and a flap like door on the bottom through which you inserted the UV impressed paper rolled up. There was a small tap to regulate a flow of drops of ammonia from the container into the box/pipe. The first kind of machine, if properly operated, was almost odourless because the ammonia vapours were distributed on the paper and the fan did take out most of what was not absorbed by the paper, the second was a nightmare, the inside of the box/pipe was impregnated with a lot of ammonia (as the copy was rolled and had to be developed everywhere) and everytime you opened the flap (to remove already developed copies or to insert one to be developed) if you didn't hold your breath and/or you weren't very quick you would taste it for good, and anyway often you opened just a little too much the little tap and the copy would be wet from ammonia.