Combine the nectarines with the sugar and lemon juice and let stand, covered, overnight in the refrigerator.
Place a colander in a large shallow preserving pan and pour in the nectarine mixture. Let the juices drip into the pan for at least 30 minutes. Remove the colander with the fruit to a bowl and bring the juices in the pan to a boil over high heat. Boil rapidly for 20 to 30 minutes, or until reduced by half. Add the nectarines and any additional juices to the syrup in the pan and continue to cook voer high heat for 10 minutes.
Carefully stir in the raspberries and cook for 5 minutes more. The nectarines will look lightly glazed and the syrup will be only slightly thickened. Ladle the preserves into hot sterilized jars, wipe the rims clean with a damp towel, and seal with new lids and metal rings. Process in hot-water bath for 5 minutes. Remove, cool, check seals, label, and store.
Makes 8 half-pint jars.
Source: Preserving the Taste by Edon Waycott (1993)