A quick job in a pin vice. Other dimensions are not critical, just leave enough room to tape your sheet of paper to the inside of the snug-fitting lid. Finally, after loading the 'film', I usually tape the lid join with black insulation tape to ensure no light leaks. In these photos, I ran out of tape so you can see a couple of light leaks around some edges. It's a one-shot process until you return to the darkroom to reload, so I made three identical cameras.
Processing is simple.
Develop the photographic paper in a standard developer, PQ Universal will do, and when washed and dried, contact the negative print to another sheet of photographic paper, face to face, to make the positive. Under the enlarger lamp, you will find that the photographic paper is transparent enough to make a good print. A couple of test exposures onto small pieces of photographic paper will enable you to find a suitable exposure time. Another photo of me with my builder Bob Algie, taking a break from adding extensions to the house in May 1999.