Chemical stability: the ability of a substance to maintain its original physical and chemical properties under the influence of chemical factors. 

The chemical stability of glass refers to the resistance of glass towards erosion by chemical solutions during the process of use such as water, acid, alkali, salt, gas, etc.  It depends on the resistance of the glass against corrosion and the type and characteristics of the erosion medium (water, acid, alkali, and atmospheric agents, etc.). 

Main factors affecting the chemical stability of glass: 

1. Chemical components

（1） The water resistance and acid resistance of silicate glass mainly depend on content of the silicon, oxygen and alkali metal oxide.

（2） When the glass contains two kinds of alkali metal oxides at the same time, some extreme values will emerge in the chemical stability of the glass due to the “mixed alkali effect”.

（3）The chemical stability of the glass will decrease when the silicon oxide in silicate glass is replaced with an alkaline earth metal or other metal dioxides. But the reducing effect is less than that of the alkali metal. 

2.  Heat treatment

（1） Generally speaking, annealed glass enjoys the higher chemical stability than tempered glass.

（2） When glass is processed with open flame in the annealing process, its chemical stability will be increased.  On the contrary, if glass is annealed in flameless fire, its chemical stability will decrease.    

（3） Phase separation will occur during the annealing process of borosilicate glass. Its chemical stability is related to the resulting structure after phase separation.  

3. Surface state

（1）  The corrosion of glass by medium occurs first on the surface, and the glass surface state has great effect on chemical corrosion resistance. 

（2） Therefore, the glass surface state can be improved with the help of various surface treatments.  

4. Temperature and pressure

（1）The chemical stability of glass varies greatly with an increase in temperature.  

（2）Pressure also has a great effect.