Sterilize 2 quart jars. Keep hot until needed. Prepare lids as manufacturer directs. Prick plums several times with a cocktail stick. Half fill hot jars with plums. Add 2 allspice berries, 2 chilies, 2 cinnamon sticks, 3 cloves and 2 blades of mace to each jar. Add remaining plums to fill jars. In a saucepan, combine vinegar and sugar and bring to a boil, stirring to dissolve sugar. Boil 5 minutes. Pour hot vinegar into jars to cover plums completely. Wipe rims of jars with a clean damp cloth. Attach lids and place in canner. Process 20 minutes in a boiling-water bath. Store in a cool dry dark place at least 1 month before serving. Makes 2 quarts. NOTE: Garnish with a fresh mint sprig, if desired, and serve with cold meats and salads.