Slice oranges in 1/4 in. slices, perpendicular to the stem/ends.
Place slices on ovenproof cookie sheet and place in oven.
Put the oven on the lowest setting (140-170F)
If the oven is too hot with the door closed, keep the door cracked.
If the oven has hot spots, be sure to rotate oranges until all slices are dry.
Remove dried slices once they are dried. Leave in slices that are still fleshy or not as dried, to dry completely.
Allow oranges to dry completely. If they are still a bit soft to the touch, give them a bit more time in the oven.
This can take between 4-6 hours. Depending on the temperature of your oven.
Allow them to cool before assembling.