Slice the oranges into 4-5mm thick slices.
In a large pot, bring 6 cups of water to a boil.
Add the orange slices to the boiling water and blanch for 1 minute. Drain and set aside.
In the same pot, combine the remaining 6 cups of water and 3 cups of sugar. Bring to a boil and stir until the sugar has dissolved.
Lower the heat to simmer and add the blanched orange slices. Cook for 1 hour, stirring occasionally.
Remove the slices from the syrup and place them on a wire rack to dry for 6-8 hours or overnight.
In a bowl, add the remaining ½ cup of sugar. Coat each dried orange slice in the sugar and shake off any excess.
Store the candied orange slices in an airtight container.