While the marmalade is cooking, fill a large pot of water, about ¾ full. Place 6 half-pint jars, upright, into the water. Ensure the jars are fully submerged, are each filled with water, and that the water is at least an inch over the tops of the jars. Cover, bring to a boil, and boil for 10 minutes. Turn off heat and leave the jars in the hot water while the marmalade finishes cooking.
After marmalade has completely cooled, if there are any jars on which the lids have not curved downward, refrigerate those jars and use the marmalade within a month.