To make dried blood orange slices, very thinly slice 1 blood orange into rounds. Lay the slices out on a baking sheet lined with parchment paper. Bake on the middle rack of an oven preheated to 175°F (80°C) for 1 hour. Flip the slices over and bake for another hour. Turn off the oven and let the slices dry out for 2 hours or overnight.