"Orthochromatic" was a fix; it had extended green sensitivity compared to earlier processes/materials (which were usually referred to as "actinic" after ortho w

"Orthochromatic" was a fix; it had extended green sensitivity compared to earlier processes/materials (which were usually referred to as "actinic" after ortho was introduced). Ortho was called ortho right from the beginning to distinguish it from what came before. The extended green sensitivity is what made it right. Or at least somewhat less wrong than things had been. If they'd found a way to create panchromatic plates/film before ortho as we know it happened, the name "orthochromatic" would have been given to that instead. So why did ortho rule the roost in the darkroom and in process photography when we had "actinic" papers around? (Obviously, panchromatic is out unless you like working in total darkness.) Incandescent lamps for exposure is a big part of the answer. You don't get a lot of blue light out of a glowing filament, and sunlight isn't quite as consistent and reliable as you might want it to be. (And arc lights aren't a lot of fun to work with or around.) Non-repro blue, a pale cyan that humans can easily distinguish but ortho film/paper can't, is most of the rest. Panchromatic can "see" non-repro blue by design, and "actinic" can see it because it's not blue enough to appear white if it's dark enough to see easily (in paste-up, etc.). Non-repro blue, ruby masks and relatively bright safelight made life... well, not exactly easy when compared to, say, a desktop publishing application, but it beat the heck out of constant squinting in the dark, wondering if that thing was really supposed to be there, or if it was a line at all.