Toronto. … but not so good politically. In the days of film, one of the tools available to the photographer was a polarizing filter. Judicious use of the filter could improve contrast and colour saturation by removing reflections from smooth surfaces.
Another major use was in colour stereo for an audience. As is well known, each eye sees a scene from a slightly different angle and the brain combines these images in 3D. Stereo viewers for individuals keep the two images separate for each eye so the brain can do its thing. Early projection of drawings and monochrome photos overlaid the two images through rad and green filters. Similar filters over the eyes (one eye with a red filter, the other with green) showed a separate image for each eye merged by the brain to show 3D once again.
Polarized filters such as described in this February 1939 article in Popular Mechanics allowed colour transparencies to be projected and viewed in true 3D colour. This was shortly after Kodachrome came on the market.
Our thanks to good friend, George Dunbar, for the suggestion and article. Nice work, George.