Blood oranges are small, sweet, nearly seedless oranges with vivid bright red flesh. They have a slightly floral flavor with berry undertones. Blood oranges are in season from December to June and are available at some supermarkets. Bon Appetit magazine, February 2009.
- Combine 1 cup sugar, 1 cup water, and orange slices in heavy medium saucepan. Bring to simmer over medium heat, stirring until sugar dissolves. Reduce heat to low; cook until orange peel is tender, stirring occasionally, about 30 minutes. Pour into strainer set over medium bowl. Chop orange slices and reserve; discard syrup.
- Combine remaining 1 cup sugar, 1/2 cup water, and lemon juice in another heavy medium saucepan. Bring to simmer over medium heat, stirring until sugar dissolves. Add chopped orange. Reduce heat to low; cook until orange is very tender and rind is translucent, about 30 minutes longer. Mix in Campari. Transfer marmalade to small bowl and cool. DO AHEAD: Can be made 1 week ahead. Cover and chill.