How Are Glass Jars Made?

Glass manufacturing begins by melting sand, soda ash and lime together at very high temperatures until a thick, sticky liquid forms. Glass manufacturers commonly refer to this substance as "syrup." When the syrup cools, it becomes glass, but while still melted, the syrup can be shaped by blowing, drawing or pressing it. Most glass dishes and containers are pressed.

Pressing uses jar-shaped molds to shape the syrup. Large mounds of hot syrup are dropped into the molds and are pressed until they fill the entire inside.

After the glass is released and cooled, it must go through annealing or tempering to strengthen it and prevent shattering. In annealing, the glass jars are reheated, then slowly cooled to reinforce the glass. In tempering, the glass is reheated, then quickly cooled with quick blasts of cold air. After this final step, the glass jars are ready for packaging and use.

Resources

• Glass Press Animation