Slice orange slices very thin, approximately 1/8-inch. A mandolin slicer may be helpful, but be sure it is very sharp.

Fill a large bowl with an ice water bath and set aside.

Add 4 cups water to a large saucepan and bring to a boil over night heat. Add orange slices and boil for 2 minutes to remove bitterness from the rind. Transfer orange slices to the ice water bath. Discard boiling water.

In the same saucepan, add remaining 4 cups water and 4 cups sugar. Bring to a boil over medium heat, stirring occasionally until the sugar has dissolved. Add orange slices and simmer for 45 minutes to an hour or until rinds are slightly translucent. Gently stir the orange slices every 15 minutes to ensure they are evenly coated with sugar water.

Transfer the slices to a cooling rack set over a large baking sheet. Dry them on the rack for 24 hours. Dip the candied slices in granulated sugar, if desired. Use immediately or store them in an airtight container in the refrigerator for up to 1 month.

Optional, dip the candied orange slices in chocolate and place on parchment paper until solidified. Also try lemons, limes, small grapefruit, or any other citrus fruits.