Suppose alot of you know this but i didnt so i thought i would share.
I had a customer ring on sunday saying we'd scratched their sills, as usual on the defensive i said, i cant see how we've done that. Anyway, went do and sure enough we had, i could see from the patterns it was the edge of the brush when cleaning the bottom of the windows. Wasnt so much a scracth more of a black scuff but it didnt look good! The frames were very old, the black seals in the windows are brown and brittle.
Anyway. Went and got some Cif, started buffing and it did make them alot better, but someone also told me to use fine wire wool, so put some cif on the sill, buffed gently with wire wool, and they came up amazing, like new.
Wish id taken some pics, customer rang me as they were out and said "they were made up, top job thank you for sorting that" nice cheap solution for something that could of cost us alot! Be careful with your brushs guys especially when cleaning the bottom part of the glass on upstaires windows. I beleive my marks were from my old vikans but i cant see this problem now with my gardiner sill brushes. I also noticed on one of the upstaires windows only half was marked, this is where i have had the brush at an angle over the porch, and the end of the brush has caught.
Hope this helps someone, it did me!