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Kodak, Fuji, and Agfa no longer manufacture type r photo material, although some is still available according to the Fuji web site. My lab, My Darkroom, is still printing Type R prints from transpancies ranging in size from 35MM up to 8x10 sheet film. We are also having to make our own chemicals, but anticipate doing these for several years. --Mydarkroom (moved from article)
This article doesn't explain why only the silver nitrate on the cyan layer is darkened for the cyan image, only the silver nitrate on the magenta layer is darkened for the magenta image, etc.
I'm unsure how to explain this clearly, let alone succinctly. While all silver salt emulsions are inherently sensitive to only blue light and ultraviolet radiation, I vaguely recall Kodak using a temporary yellow dye in these emulsions: the top layer was an "ordinary" emulsion, inherently blind to all light except blue light. Under that, a yellow dye layer (present during exposure and removed during development) kept blue light from reaching deeper into the emulsion's stacked layers. The next layer was an "ortho" emulsion, sensitive to blue light that never reached it because of the temporary yellow dye layer and sensitized to see green light. Under that was a final emulsion layer, sensitive to blue light that never reached it because of the temporary yellow dye layer and sensitized to red light.
I should find the binder in my Connecticut barn that contains the Kodak technical publications from the 1980s that explain this, and cite them here. These Type-C chromogenic prints are classic "negative working" photographic materials: more exposure to light causes more dye formation during development.