These glasses are made by replacing small ions in the surface zone of the glass with larger ions, thus puffing the surface into compression as with heat-treated glasses. In a typical manufacturing process a sodium-containing glass is heated to just below the transformation temperature in a solution of molten potassium salt. Sodium ions transfer into the salt, and are replaced by potassium ions with a thirty per cent larger radius. If a depth of about 1 mm is affected in this factor of five or six. Provided the compression is sufficient to be maintained when the glass is loaded, surface blemishes within the skin depth are inhibited from developing as cracks. This enables the glass to be used to higher levels of tensile stress, with strengths comparable to aluminium alloys. The process is very slow and more suitable for thin glass which is difficult to toughen thermally. Current uses include toughened ophthalmic lenses and electric lamps.

Chemically strengthened glass is prepared by replacing metal ions in the glass surface layer with those in the surrounding molten salt thus forming a compressed surface layer. This product is highly regarded for its high strength, good thermal stability, high degree of smoothness, no deformation, no self cracking and its simplified procedure to handle widely varying tasks such as extra thin strengthened glass, special-shaped strengthened glass and large-area strengthened glass.

2.Application
Chemically strengthening glass technology overcomes the disadvantages of thermal tempering for its excellent optical properties that suits optical specialized applications such as wind-shield in air planes or automobiles, high-grade architectural glass, paned of optical instruments and panel of electrical appliance.

3.Performance
Surface compression: 330¡«410MPa; Resistance of bending: 200¡«350MPa; Resistance of impacting: 3.5¡«4.0m(227g steel ball); Thermal stability: 150oC; Non-deformation; Non-distortion

Like the toughening process, Heat Strengthening imposes limits on the maximum glass sizes.

Wired glass, some patterned / figure rolled glass cannot be Heat Strengthened.