I looked in the archives for alum in relation to broken drill bits
Try a Drug Store for Alum. Yes it will work on broken drill bits
in Silver. The Alum needs to be heated in a Glass beaker with the
piece of jewelry placed in it.
If you can't get hold of any alum from the drug store, some people
use similar chemicals (often called alum but strictly not alum by
definition but still contain the sulphates required) as their pickle
solution, such as sodium bisulphate (often sold as pH down).