how to remove stains in glass window?

Answer 1

Try to use lemon. It's safe!

Answer 2

Are stains "in" the glass or "on" the glass? Glass has a high surface tension so there are many things that will break that tension and "wash of" most stains. Vinegar may be better than the lemon idea. A solution of baking soda and table salt also works on paint and varnish stains. Stains "in" the glass can some times be removed with heat from a butane torch, for example.