| The "graphics arts cameras" they are referring to are pre-digital. They looked like this: http://www.forgottenartsupplies.com/?what=artifacts&image_id... The goal was to compose a layout into a single image. You created a layout by literally cutting and pasting things onto a board. Then you placed that board in the area at the bottom and took a picture of it that was transferred to film loaded in the top. You're right that the film was special; but it's the other way around from how you were thinking. The film was not sensitive to red light. To this film, red is "black" and cyan or blue is "white". Why this was useful: - You could open the box of film (it came in sheets) in a room that was darkened except for a red bulb, without exposing it. - You could use overlays of transparent red material (rubylith) to mask things precisely. Even though you could see through to the layer below, the camera would see it as all black. - And, as the article mentioned you can add notes to the layout with blue pencil and it would be invisible to the transfer. We always called this "non-repro blue" though, as in, the camera wouldn't reproduce it. |
-- Litho film was also very high contrast so everything pretty much came out black or white. (Photos weren't actually reproduced as greyscale but rather as a set of larger or smaller black dots using a halftone screen. This still applies when things are printed.)
-- Because litho film was sensitive to blue, the non-repro blue writing on the white paper would, like the white itself, be an exposed part of the image. This results in a black area of the negative where silver halide has been turned into metallic silver. This black area would then become white again when the negative was used to create a printing plate.