The plates used to make these prints are hand-laminated (Imagon brand) or pre-coated (Solarplate brand) with a photosensitive polymer. Exposure to ultraviolet (UV) light through a transparent positive photographic image causes the polymer to harden differentially, depending on the amount of UV transmitted through the positive. Developing the plate in water (or in the case of Imagon, a mild alkaline solution) dissoves the unhardened polymer, forming minute grooves and pits that hold the printing ink and thus form the image on the plate. Finally, the inked and wiped plates are printed with high pressure onto damp paper by means of an etching press.
This process is similar to photo-etching methods such as photogravure, but no acids are used (hence no "etching", just "developing").