This involves the material and composition of glass, and the main raw material for making glass is SiO2 and quartz.
Glass is amorphous solid obtained by melting, cooling and curing. Its structure has certain rules (short range order) in the atomic and molecular scope, but no rules (remote disorder) in the macroscopic scope. It can rely on mould to make various shapes. The irregular structure of glass determines the following characteristics of glass:
1.Isotropic, glass particle arrangement in general is irregular, but is statistically uniform, therefore, its physical and chemical properties are the same in any direction. The crystal is anisotropic. Examples: resistivity, thermal conductivity, transmittance and refractive index.

2.there is no fixed melting point, and glass changes from solid to liquid in a certain temperature range. The crystal has definite melting point, for example, ice (water crystal) melts at 0 C. This characteristic of glass enables it to be shaped by blowing, pulling and pressing.

3.The composition and properties of glass can be adjusted. The properties of glass can change continuously and gradually with its composition in a certain range. Crystals have fixed components and definite properties. In this way, we can adjust the composition of the glass, so that its performance meets the requirements of use.
Generally, glass is fragile because of its coarse crystalline grains, not tightly bonded with each other, it is easy to loose in crystal structure, cracks are easy to expand, which is the principle of glass knife cutting glass.