At one point in history, blueprints were actually blue. Now, if you even see a dead tree version of plans or assemblages, they’re probably printed off with a plotter or large format printer. You can, however, make your own blueprints at home, as [Tyler] shows us in his Hackaday Project.

Back in the olden days, master drawings were traced onto large sheets of transparent film. These master prints were then laid over paper prepared with Potassium Ferricyanide and Ferric Ammonium Citrate to create an insoluble Prussian Blue background for the prints. Developing is easy – just expose the transparent positive and undeveloped paper to UV light, in the form of fluorescent bulbs or the sun.

[Tyler] began his blueprint creation process by getting a few design sketches of the RSI Aurora and Nautilus, editing them on a computer, and printing them out on transparency sheets. A solution of equal parts Potassium Ferricyanide and Ferric Ammonium Citrate were painted onto a piece of paper and allowed to dry. Exposing was a simple matter of laying the transparency over the undeveloped paper and setting it out in the sun for 20 minutes or so. After that, it’s a simple matter of washing off the unexposed chemicals and letting the newly created blueprint dry.

It’s a simple technique, but also very, very cool. Not exactly practical, given a plotter can spit out an architectural or assembly drawing of any building, vehicle, or device in a few minutes, but just the ticket for art pieces or extremely odd engineers.

Thanks [Sarah] for sending this in.