I remember the first time I came across these jars. I was invited by an older Lady to look at and buy some of her items, and included were a few of the new-to-me jars with a hole in the bottom. She explained to me that she and her sister had a Tea Room back during the Depression, and the jars were used on a daily basis for serving preserves. She went on to tell how they had jars of homemade jam or jelly sealed with paraffin on the top. After running a knife around the paraffin, they would empty the entire contents directly into these jars with the paraffin at the bottom covering the hole