Physical tempering and chemical tempering are two different methods of strengthening glass.

Physical tempering, also known as thermal tempering, involves heating the glass to a high temperature and then rapidly cooling it using forced air. This creates a state of tension within the glass that makes it stronger and more resistant to breakage. Physical tempering can be used on a variety of glass types, including soda-lime glass and borosilicate glass.

Chemical tempering, on the other hand, involves immersing the glass in a chemical solution, usually a molten salt bath, which replaces smaller ions in the glass with larger ones. This process creates a layer of compressive stress on the surface of the glass, making it stronger and more resistant to breakage. Chemical tempering is typically used on specialty glasses, such as quartz and sapphire, that cannot be thermally tempered.

The main difference between physical and chemical tempering is the method used to create the internal stresses within the glass. Physical tempering uses thermal shock to create a state of tension, while chemical tempering relies on ion exchange to create compressive stress on the surface of the glass. Additionally, physical tempering is typically used on a wider range of glass types, while chemical tempering is more commonly used on specialty glasses.