Line a 9x13 pan with paper towels, this is where you'll set your orange slices after slicing them and will help release some moisture.
Using a serrated knife, slice oranges to about a 1/4 inch or 1/8 inch thickness. Line into pan and top with more paper towels each layer.
Transferorange slices to a foil or parchment paper-lined baking tray.
Bake for about 3 hours at 250ยบ, turning them over every 30 minutes to dry evenly.
Once done and cooled, you can poke a hole in each one with a wooden skewer. Tie twine around each one to make ornaments or string together to make a garland.