Place the orange peels in a pan of cold water to cover and bring to a boil; drain. Repeat this process three times to remove some of the bitterness from the pith, using fresh cold water each time.
Combine 12 oz/340 g water, the sugar, and corn syrup in a heavy-bottomed saucepan and bring to a boil, stirring to dissolve the sugar. Reduce to a very low simmer, ad