I have just removed a broken Tap from brass and used a stainless steel spoon to stir the solution.
The Stainless steel discoloured to a dull sheen. Uncertain as to how long it will last but is difficult to remove the sheen with stainless steel scourer.
The solution used was Saturated solution of Alum in water apllied over low heat
Alum is available from the swimming pool section of hardwares and may be found as a flocculent and contains Aluminium Sulphate as an active constituent.
Phil