One of my students is doing this right now. The paper ISO is quite slow, as mentioned, and the size of the aperture will make a big difference as well. I have a Daylab 4x5 pinhole camera with an f/stop of about 258, as I recall; it accepts 4x5 film holders, so I sometimes cut Ilford papers to 4x5 and load the holders with that. Exposures in bright sunlight vary from 10 to 60 seconds, depending on shady areas, etc. In darker conditions the times might run to 10 to 30 minutes.
My student is exposing paper in home-made pinhole cameras - the usual oatmeal box, Pringles can sort of thing - with much smaller pinholes, made with a #10 sewing needle. His exposures vary widely, since he's done some indoors that took almost 2 hours, some outdoors that took 30 minutes. Those times are obviously due to the size of the pinhole apertures, and will vary widely as lighting conditions, type of paper, and f/stop are changed.
When making a paper positive from a paper negative, the process used for making photograms works quite weil. Take fresh photo paper, place it emulsion side up under your enlarger with the lens set at f8, place your paper negative emulsion side down on top of it, and place a piece of clean window glass on it, just as you would if you were making a contact sheet.
With a heavy piece of cardboard, cover all the negative except about an inch, and expose for 5 seconds. Move the cardboard to uncover another inch of the negative, and expose that for 5 seconds. Continue in this fashion until all sections of the paper have been exposed in 5 second increments. Develop this test print, and use the best exposure to make your final print. (As with any process, you might need to adjust these test strips for more or less time for best results.)
Develop, wash, and dry as you would any other photograph.
Paper negatives are a great deal of fun, and are akin to the first attempts at photographic processes. They are a bit frustrating to work with at first, until you practice a bit, but have a wonderful quality unique to themselves when you work with them awhile. If/when you have success doing this, a nice touch for a vintage look is to soak the print in coffee or tea, for a nice sepia quality.
I have to add I'm no expert, and I'm certain there are many others out there with better/faster/easier/fancier/cooler methods for doing this, but this ought to get you started!
Mark
