I was making apricot jam using fresh apricots and gelling sugar. All went well except I burnt it. Some of the solid parts sank to the bottom and stuck there. After putting the good stuff in jars, I then soaked the pot.
About five hours later I went to scrub it and the whole bottom layer came free in a perfect circle. The under side is shiny — looks like plastic. The upper side is matt and almost furry. As it dries out it is curling up and is brittle.