At Dental colledge we used to cast lead/tin mix in plaster moulds,make the item in wax,,cast a plaster mould around it with suitable points for pouring in the the lead/tin mix in,let it set,boil out the wax with a kettle then wash with detergent,let the mould dry,then slowly heat the mould in an oven(so it doesn`t crack when you pour in the lead/tin mix,or lead in this case),while mould is heating/drying heat your lead/tin mix until moulten,when ready for pouring,sprinkle a little borax on the lead to clear the dross,and scoop off,then your ready to pour your lead/tin mix,lead in this case of course,pour very slowly or you will get a blow back which will mean a trip to A+E,then just leave to cool for a couple of hours.