I'm a Plumber, I was trained by my Master Plumber 28 years ago and how to lead in cast iron joints. I leaded joints like crazy the first five years before newer drain materials came out. Here are some pointers
Pour lead out side with a small fan to move the vapors away.
use a good pot to pour
get good quality lead-- plumbers lead is super clean / less tin in the lead
No children around to distracted or touch the lead
I pour all my lead drop shot, spinner baits, jigs, darter etc... in the summer on dictated whole day of pouring
long sleeve and mechanic rubber gloves for handing the lead after cold to trim excess lead
Good luck!