Preheat the oven to 175°. Set large wire racks on each of 3 large rimmed baking sheets. Arrange the orange slices in a single layer on 2 of the racks. Dry the oranges in the upper and lower thirds of the oven for about 4 hours, until the flesh is slightly tacky and the peel is crisp; flip the orange slices and shift the pans from top to bottom and front to back halfway through drying. Let the slices cool completely on the racks.
Meanwhile, trim the ginger as necessary to fit the width of a mandoline. Slice the ginger into lengthwise strips 1/8 inch thick; discard the end pieces. Arrange the ginger in a single layer on the remaining rack. Dry the ginger in the oven for about 3 hours, until dry to the touch; flip the ginger and shift the pans from front to back halfway through drying. Let the ginger cool.
Divide the oranges, ginger and spices into 8 bags and secure with twine.
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