The Original post was for lime scale, now wire wool is fine for this so long as its kept wet.
Now if you are going to use wire wool as a scraper then you are asking for trouble.
If I was going to have three young lads working for me, to clean the deposits off the windows, then I think training come's to mind,
letting three young lads loose with wire wool on windows has ended with the results I would expect.
If you use a scraper first to remove, cement, or any size deposit, once you have it flat, any stain can be removed with wet wire wool.