POP stands for Print-Out Paper. Technically I should have written P.O.P. It is -- or more likely these days, was -- a very slow photographic paper that darkened gradually upon exposure to light -- UV, was the key, I believe. Strong light was best, like daylight. The resulting images were brown/sepia in color. In Zaire I had lots of light, generally speaking, and so all I needed was a sheet of glass and a tray for fixer. More info is available by googling Print Out Paper.
must have been fun trask !
centennial POP was the last made, it was taken over by harman/ilford IDK 10-12 years ago
and eventually its production ended. since then people have been trying to figure out a way
to convert regular photo paper into POP paper by soaking it in potassium nitrate and other fun chemicals
so the image would appeaer on the paper and and then fixed with regular fixer, or a buffered fixer
( sodium thiosulfate with a bunch of sodium carbonate (washing soda ) in there. usually the POP prints were
toned in gold or selinum or other fun things i think they were purplish otherwise but i might be remembering sometrhing different.
there have been threads here on apug about converting photo paper to POP
a guy named lars m... ( can't remember his last name, from sweden i think ) had some successes, NedL has also been doing it
and has had some successes. i gave up on preserving the images but i make them anyways, and use the electric beam to preserve them.
YMMV