Wash and pick over the blackberries. Put the vinegar into a stainless steel pan with the sugar and heat gently, stirring well until it has dissolved. Add the blackberries and simmer gently for 5 minutes. Do not allow the fruit to become too soft or to break up. Remove the blackberries with a perforated spoon and pack into hot, dry, sterile jars with non-metal lids. Keep warm, Boil the vinegar until it is syrupy. Put a geranium leaf well down in each jar and pour the hot syrup over the fruit to cover completely. Seal. Keep at least 1 week before eating. The geranium leaves give the pickle a delicate scent.
