Remove peach skins, then put fruit through a food chopper. Weigh, add the peach juice, bring slowly to a boil, add sugar, and over high heat stir gently but continuously to keep from scorching. When the jam tears off the spoon, remove from heat and let stand 3 to 5 minutes, again stirring gently to dissolve froth and foam.
Pour into hot jars, leaving 1/4 inch headroom; simmer at 180°F (82°C) in a hot-water bath for 15 minutes. Remove jars; let cool upright and naturally.
For spiced jam: to this rule add a spice bag containing 3 inches of cinnamon stick, broken; 1 tsp whole allspice; 2 tsp whole cloves; and 1 tsp of minced fresh gingerroot. Remove the spice bag before filling jars.