Mix the sugar and spice (and all things nice) in a small bowl.
Using a madoline or sharp knife, slice the oranges as thinly as possible then place on wire racks over baking trays.
Sprinkle oranges with the sugar and spice mix, reserving some for later; and place in oven for 2 - 4 hours. The thickness of the slice of orange will determine cooking time.
Remove from oven and sprinkle with reserved sugar.
Store in an airtight container in a cool place. I keep mine in the pantry.
Notes
Dehydrated oranges make a delicious addition to many recipes, can be used as a garnish or decoration. My batch has been stored for around 6 weeks without any sign of deterioration.