Given up on chemical tests , no consistency/ lack of differentiation.
Mortar and pestle idea goes no where.

Had to decide this week whether a 2003 board had failed solder due to SnPb
or PbF and excess heat , where it was used. Could not decide by appearance,
good mirror finish, lack of pastiness but solder joints too shallow to tell
domed from conical, so probably SnPb.
Low temp soldering iron test, melted - SnPb
Paper test - SnPb
and indentation test much nearer Pb diameter than Al so - SnPb