Preheat the oven to 200℉. Line baking sheets with parchment paper, and set aside.
Slice the oranges about ¼-inch thick. Lay the orange slices in a single layer on the prepared baking sheets. Bake for about 2½ to 3½ hours, or until translucent. The amount of time you need to bake them depends on how thinly you cut the slices. If you have more than one baking sheet, you may want to change their positions halfway through baking. Also... I found that turning them over toward the end of their baking time ensured that the slices were dried-out on both sides.
Store your dehydrated orange slices in glass jars. They should last in the refrigerator for a substantial amount of time. The author stated that her research says they can keep in the fridge for up to to years. I would guess that you would use these up long before that!
Notes
To make in a dehydrator: Lay out the orange slices on the stackable dehydrator trays. Set to 130 degrees F and let the orange slices dehydrate for about 2 days. Depending on how dried out you want them to be, and how thickly you sliced the rounds, check for more or less time. They should be pretty translucent, when done.