Blueprints are cyanotypes, you might find more information searching for websites describing them. You might want to see AlternativePhotography.com, they describe cyanotypes as well as other non-standard and obsolete types of photography.
One-time use cyanotype mix:
Take about 1g of ferric ammonium citrate (here’s a 10g bag from Photographers’ Formulary), 1/2g of potassium ferricyanide (same place, same amount), and 16mL of water, and mix them together in subdued light (it doesn’t need to be all that dark, just out of the sun). This is your emulsion, enough for four 8x10 pictures.
Take your emulsion and brush about 2mL of it onto whatever you want to take the picture on (paper, glass, cloth, what have you). Let it dry in a warm, dark place. Add another coat with 2mL more after the first coat dries, and let it dry as well.
You’ll want to make the film just before you take the picture, it will mold if you wait too long.
Now, put the film on your enlarger (or in front of your projector or however you’re making this print), secure it so it doesn’t move around (it’s going to be there a long time), and start exposing it. Keep exposing it until you see the image burned onto the film in gray and yellow. This is hardly an exact science using homemade film and a makeshift printer, you’ll might need to try it several times to get the timing right, but expect it to take a few hours.
Once you can see your image and it’s exposed how you want it, take it off the enlarger and put it in a bath of running water. The gray will turn blue and the yellow will wash off in about a minute. To get a more vibrant blue, add some hydrogen peroxide to the water at this point–how much depends on how far you want to go, but don’t use too much or you could wash-out your image–and let it soak for five or so seconds more.
Your print is done, you just need to let it dry now.