Stir together the raspberries and 1 cup of the sugar in a medium bowl and let stand for 1 hour.
Stir the cranberries and the remaining sugar together in a nonreactive shallow preserving pan and place over high heat. Stir constantly so the sugar does not burn until the cranberries begin to release juice, about 5 minutes. Continue cooking until all the cranberries have popped and the mixture is syrupy and comes to a boil. Skim off any foam that forms on top and continue to cook and stir until the mixture thickens, about 10 minutes more.
Add the raspberries and all their juice and cook for 10 minutes more. Stir in the orange juice and zest.
Remove a small amount of the jam to a saucer and place in the freezer for 5 minutes. If the mixture wrinkles when pused to one side, it is ready. If not, continue cooking for 5 minutes and retest.
When the preserves are the right consistency, turn down the heat to a simmer and ladle into hot sterilized jars. Wipe the rims clean with a damp towel and seal with new lids and metal rings. Process in a hot-water bath for 5 minutes. Remove, cook, check seals, label, and store.
Makes 4 one pint jars.
Source: Preserving the Taste by Edon Waycott (1993)