Hello, I'm an expert in materials science with a focus on glass and its applications. When it comes to canning jars, it's important to understand the properties of the glass used in their construction.

Canning jars are typically made from a type of glass known as tempered glass. Tempered glass is a safety glass that is processed by controlled thermal or chemical treatments to increase its strength compared to normal glass. This process creates a glass that is about four to five times stronger than standard glass.

The tempering process involves heating the glass to a high temperature until it softens, and then rapidly cooling it. This causes the surface of the glass to contract and harden, while the inside remains in a more elastic state, creating a layer of compression on the surface. This compression makes the glass more resistant to impact and less likely to break, and when it does break, it shatters into small, less sharp pieces, reducing the risk of injury.

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Glass Containers > Glass Jars > Mason Jars. Mason jars are thick-walled, wide-mouthed jars made of heat-tempered glass. They are able to withstand the heat and pressure associated with water bath and pressure canning.read more >>