Wash the blood oranges and cut the stem end off of each one. Slice the oranges into 1/4” thick slices, poking out any seeds that you come across.
Cover the orange slices with water and bring to a boil. Simmer until the peel is tender, about 15-20 minutes. Drain.
Prepare for canning: Wash the jars and flat lids. Put the jars in the canning pot and cover with hot water. Heat over high to bring to a boil and keep the jars hot.
Wrap the cloves and allspice in a piece of cheesecloth and tie it off so that the spices are contained. Rinse out the pan or use a new large saucepan before proceeding.
Stir the sugar and water together over medium heat until the sugar is dissolved. Add the spice bag and the orange slices to the syrup. Cook, stirring occasionally, until the fruit is glazed and somewhat translucent, 30-40 minutes. You’ll want to remove the spice bag after the first 20 minutes.
Line the hot jars up on a folded towel.
Pack the orange slices into the jars, leaving a generous 1/2" of headspace. Spoon the syrup over the slices, again leaving 1/2" of headspace. Slide a wooden or plastic chopstick around the inside edges of the jar to remove any air bubbles.
Use a clean towel to wipe any syrup off the rims, then top each jar with a lid and tightened ring. Place the jars back in the canning pot and make sure they are covered by at least 1 inch of water. Bring to a boil and process for 10 minutes for half-pints, or 15 minutes for pints.
Remove the lid from the canner and turn off the heat. After 5 minutes, transfer the jars to a folded towel and allow to sit, undisturbed, for 24 hours. Check the seals of the lids after 1 hour. If a seal has not formed, refrigerate the jar immediately.
You may have some extra syrup leftover. Store it in the refrigerator and mix it into cocktails or seltzer, or spoon it over ice cream!