Question

give reason why window glass of old building look milky

Answer 1

Heat difference of day&night which may convert amorphous to some crystalline form in glass.

It is a slow process, due to the flow of glass particles from top to bottom (very slightly).

Hence, it looks faded in an old building.  

Heat difference is due to continuous exposure to the sun in day& cooling process in nights.

Answer 2

glass is considered as a supercooled liquid because it a blowing property which flows from higher level to lower level old glass become ml anaelization