I do know that. Starting in the 50's, the commom material used became polyvinyl chloride
These started in the 50's, but they are pretty much identical tho those.
Are you familiar with phonograph records? I've never heard of them. Yes, I have heard of them. They are a medium to store analog sound which is known as Gramophone in British english, did you know about that ? I had no idea. What else do you know about them? Well, I also know that the grooves start close to the periphery of the disk and only ends close to the center Very interesting. Do you know what they are made of ?
At first, the discs were commonly made from shellac; starting in the 1950s polyvinyl chloride became common.