P.O.P. (Printing-Out Processes)

The term “printing out paper” and the associated initials P.O.P. were introduced in 1891 by the Ilford Company for their gelatin-chloride papers. The term has since been applied to any paper that requires ultra violet light to form a complete image.
The basic light-sensitive substance used in all of these papers is silver chloride with an excess of silver nitrate. Once the image has been printed and toned, the rest of the procedure is like handling a silver print. It is fixed, washed, dried, and preserved in the same way.