Place the berries and sugar in a large bowl. Gently stir together and let sit for 10-15 minutes. In a large nonreactive saucepan, gently stir together the berries and lemon juice.
Bring to a boil, reduce the heat and cook, uncovered, stirring frequently and removing any foam, until the jam has thickened, about 15 minutes. It will continue to thicken as it cools.
Ladle the hot jam into sterilized jars, leaving ¼ inch of headspace. Remove any air bubbles. Wipe the rims clean and seal tightly with the lids. Put the jars in a boiling-water bath for 10 minutes.
Make sure the jars are covered in water. The sealed jars can be stored in a cool, dark place for up to 1 year. If a seal has failed, store the jar in the refrigerator for up to 1 month. Makes 6 half-pint jars.