Preheat the oven to 200°F to 225°F
Wash the oranges thoroughly
Pat the oranges completely dry
Slice the oranges into thin, even rounds
Remove any seeds
Line a baking sheet with parchment paper or a silicone mat
Arrange the orange slices in a single layer
Blot the slices with paper towels to remove excess moisture
Place the baking sheet in the oven
Keep the oven door slightly open if needed to allow moisture to escape
Bake for 2 to 4 hours
Flip the slices every 30 to 45 minutes
Check for dryness and reduce browning as needed
Remove the slices when they are dry and no longer sticky
Let the slices cool completely
Store in an airtight container once fully cooled