For some reason this did not work as it was supposed to

Maybe the burner removed all the oxygen needed for the process.
By the way, Pb3O4 is really (PbO)2PbO2, is there any particular reason for using Pb3O4 and not PbO.
When I tested it in the lab they colour the flame in the same way when burned.
I will keep looking, and return if I find anything useful.