This section is from the book "Preserving And Pickling", by Mary M. Wright. Also available from Amazon: Preserving and Pickling: Two Hundred Recipes for Preserves, Jellies, Jams, Marmalades, Pickles, Relishes and Other Good Things.
Prepare a syrup, allowing one pound of sugar to one of plums, and to each three pounds of sugar one pint of pure cider vinegar. Simmer twenty minutes. Allow four tablespoonfuls each of whole spices, cinnamon, broken in pieces, cloves and allspice, one tablespoonful of blades of mace, to peck of ripe plums. Prick the plums. Add the spices to the syrup, and pour over fruit boiling hot Let stand in stone jar three days, then drain plums from syrup. Put into quart fruit jars. Place syrup in porcelain-lined kettle and boil down until quite thick, and pour over fruit until jars are full. Place covers on jars and seal. Let stand until cold, then try tops to see if air-tight Put away in a cool, dry place.