Fill a large canning pot with water and bring to a boil.
Center a new lid on a jar of marmalade, apply the ring band, and tighten it fingertip-tight.
Carefully place the filled jars onto the rack in the canner, making sure the water covers the jars.
Place the lid on the canner and bring the water to a full, rolling boil.
Boil for 10 minutes before removing the jars to a tea towel
Let the jars cool undisturbed for 12 hours to allow the seal to set.
After cooling, check the lids by pushing down on the center; if the lid doesn't move, it's properly sealed.
Store the jars in a cool, dry place for up to a year. Once opened, store in the fridge and use within 1 month