I came across this window on a lighthouse while on vacation in Washington. The setting was beautiful, but the window looks horrible and it really mars the view. I would guess that this window hasn’t been cleaned in a couple of decades. This kind of buildup typically doesn’t just wipe off with a little soap and water and elbow grease.
The exterior surface of the glass will likely need to be restored, which may involve polishing. Polishing on old glass like this will remove some of the beautiful innate waviness of antique glass and take away from its character.
Don’t let your windows get like this. Take care of them, enjoy your views and show off your home!