Question

why do glasses turn milky ,when become old ??

Answer 1

Glass is an amorphous solids and it is also called supercooled liquid.Hence like liquids it has tendency to flow. therefore in old the glass look milky in appearence or thicker because glass over the years flown down under the influence of gravity.

Answer 2

Hence glass is considered a super cooled liquid and that becomes the reason why the glass windows become slightly thicker at the bottom that at the top over a period of time and turns little bit Milky.Explanation: All amorphous solids have tendency to flow as rubber, plastic etc...