Pound together saltpetre, prunella salt and 1 lb. common salt. Rub this mixture well into the meat and lay in a large tub, turning frequently for 2 days. Put all remaining ingredients into a saucepan, bring to the boil and remove all the scum. Allow to boil for 15 minutes, then pour over the meat while still hot. Leave the ham in the pickle for 3 weeks, rubbing and turning it daily. Remove the ham from the pickle, leave to drain for 1 hour then cover with dry sawdust before smoking for about 3 weeks.