Just a couple of days ago, for some reason, I suddenly recalled how my mother, her sister, their mother, and their mother's sister (my great aunt) used to get together to can. And in particular I recalled how, when they canned jams, they would pour hot melted wax over the top of the jam in the jar prior to adding the cover. When you were ready to eat the jam, you simply removed the cover and pulled the solidified wax disk off of the top of the jam.