Firescale on silver is caused by Cu2O embedded in the polished silver which can only be removed by abrasion. Sometimes a 'bright dip' may help by dipping is repeatedly into HNO3 and water but HNO3 dissolves the silver as well, I tried this a few times with moderate success.
On this page http://en.wikipedia.org/wiki/Cu2O I read that hydrochloric acid dissolves Cu2O, so I am eager to try this to (boil ?) the work in HCl acid after the Tripoli polishing step tp let dissolve the firescale and then fine polishing the work.
Does somebody have experience with this ?