Hi Han,
I've got a beach-side holiday home where the windows are blasted by wind, rain and salt spray.
Within a few years of building it an impervious kind of deposit built up on the glass and no amount of window-washing would remove it. I heard about using steel wool and diluted detergent, and gave it a try, with complete success. I think I used the softer aluminium type 'steel' wool.
B22.
