Toronto. Since photography began there was always some means to keep the plates or film protected from the light. When the Leica and its competitors arrived. Leitz made a very heavy and elaborate reusable cassette that opened only in-camera as the Leica base was locked.
August Nagel invented the single use cassette with a velvet light rap at the opening for his company’s Retina cameras. The idea caught on, especially after Kodak embraced it as a standard for retail outlets selling unexposed 35mm film rolls in 20 and 36 exposure reels (later 24 exposure). Leitz justified their expensive reusable cassettes by touting their open aperture meant no “tram tracks”. The “free” one-use cassette with its velvet trap had a very very small risk of scratching the film (tram tracks) but the risk was mostly if a cassette was left out of its wrapper or canister in a dusty area before use.
NB. The title of this post is a riff off a 1979 book “The Keepers of Light” by William Crawford. This excellent book of photographic history and practical advice on old processes is available here at no cost. It can be read online or downloaded in various formats.