The surface of the glass is slightly rough at the initial stage of moldy.
Although the mold is not visible to the naked eye, the glass is more difficult
to clean and easy to stain.Then there will be small spots, flakes, filaments
and misty spots will appear gradually.
Moreover the rainbows will appear and the hand feel is rough, the smoothness
and transparency of the glass are significantly reduced.
Weathering of the glass surface first manifests itself as the glass surface reacts
with moisture in the atmosphere
That is: ≡ S i ― O ― N a + H ₂ O → ≡ S i O H + N a O HThe result of the reaction makes the glass surface alkaline and produces tiny
spots/spots on the glass surface, also known as alkali evolution.
Research has shown that: when the PH value of the glass surface is greater
than 9, the alkali starts to attack and dissolve the basic silicate network.
The reaction formula is as follows SiO ₂ + 4 N a O H = N a ₄ S i O ₄ + 2 H ₂ O
The process of this reaction caused the glass network structure to be eroded
and damaged, causing the glass to produce roughness, rainbows, and a drop
in transmittance.