3 pounds firm plums, cut into eighths and seeds discarded
1/2 cup water
1 tablespoon lemon juice
7 1/2 cups sugar
1 (3-ounce) package commercial pectin
In large non-aluminum kettle, combine plums, water, and lemon juice. Bring mixture to boiling over high heat, stirring constantly. Reduce heat to low and cook, covered, 10 minutes or until soft, stirring occasionally. Mixture should have reduced to about 4 1/2 cups.
Add sugar and heat mixture to full, rapid boiling over high heat, stirring constantly. Stir in pectin; return to full, rapid boiling and boil exactly 1 minute, stirring constantly. Remove from heat. Set aside 1 minute and skim off any foam that has formed.
Meanwhile, sterilize 8 half-pint jars or jelly glasses and the necessary lids, and bands, according to manufacturer's directions. Divide jam among sterilized jars, leaving 1/8-inch space at top of jar. Wipe rims of jars to remove any jam and seal with lids and bands.
Process jars in boiling water for 5 minutes. Remove jars, label, and store in cool, dry place