Tempering is divided into physical tempering and chemical tempering. Tempering is to heat the glass to a certain extent in a tempering furnace, and then cool it down, and the hardness of the glass will increase after tempering.

Physically tempered glass refers to the process of heating flat glass and then quenching it, so that the surface layer of the cooled glass forms compressive stress and the inside of the glass forms tensile stress, so as to improve the strength of the glass and make ordinary annealed glass into tempered glass.
Physical toughening does not change the chemical composition of the glass.

Chemically tempered glass is to place the glass in molten alkali salt to exchange the ions in the surface of the glass with the ions in the molten salt. To achieve the effect of improving the strength of glass.