now...lets deal with this
you don't need anything so harsh.
Get a cup of water- and 3 sheets of kitchen roll tissue or a rag if you can rinse it clean daily.
Lets assume kitchen roll.
Dampen a folded piece of kitchen roll in the water, dip it into the cold ash from yesterdays burn and use it like a paste. It is gently abrasive, less than wire wool and it seems to work better than anything I have ever tried.
Keep the tisse damp and dip it in more ash as you need. Use that to clean the entire window.
once it's soot free but smeared to hell with ash, use a clean wet sheet to wipe it off and the last one dry to buff it to a shine.
Clean