Walnuts for pickling must be young, green and easily pierced with a fork. Prick walnuts all over (it is advisable to use gloves when doing this as they stain badly) and put into a brine solution made with 1 lb. salt to 2 pints water. Leave for 9 days, changing the brine every 3 days. Drain walnuts, spread on a tray and leave exposed to the air until they are quite black. Pack into a jar and cover with the cold spiced vinegar. After a couple of days, top up the vinegar and seal. Leave for 1 month before using.