response: I do know that. Starting in the 50's, the commom material used became polyvinyl chloride
original_response: These started in the 50's, but they are pretty much identical tho those.
history: 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 ?
knowledge: At first, the discs were commonly made from shellac; starting in the 1950s polyvinyl chloride became common.