Toronto. Did you ever wonder how negatives were converted to positive images – where white was white and black was black? The key was to process the negative, then bleach the film rather than fix it (removes only the developed silver), expose the remaining silver halides, develop again and then fix the film.
This was most commonly done with amateur movie film creating a positive print for projection. Decades later, three layers of dyes and colour couplers in the colour film tri-pack transformed colour negatives to colour positives – either amateur movies or transparencies (slides).
In the January, 1929 issue of Science and Invention magazine, a system used for the commercial processing of amateur B&W negative film into B&W positive film ready for projection is shown and explained.
Thanks to friend George Dunbar for sharing this tidbit of photographic history with me. Nowadays we make videos in full colour on smartphones ready for sharing with friends beside you or around the world. And with nary a bath or external process in sight! How times have changed.