It's not a recommended practice anymore, according to the University of Missouri Extension office, but some makers of homemade jam still use wax to seal their jars. The paraffin wax is melted, then poured across the top of the jar so it creates a thin, protective layer. The purpose of the wax is to prevent mold growth, but it doesn't always work. To get the wax seal off your jam to use it, all you need is a sharp paring knife.
Insert the end of the knife blade into the edge of the wax, along the inside rim of the jar. Hold the knife so it's standing straight up.
Run the blade slowly all the way around the wax seal to loosen its edges from the glass. The wax is normally only about 1/8 inch thick. If you try to loosen it too quickly, it can break apart and crumble.
Place the end of the paring knife blade under an edge of the wax. Lift the seal up and out of the jar of jam. Check the top of the fruit for any remaining pieces of wax. Pick them out with the end of the knife.
Reseal the jar of jam with a metal lid and store the remaining contents in the refrigerator.