Combine grape juice, lemon juice and pectin in a three-quart microwave-safe bowl. Cover with plastic wrap or waxed paper and bring to a boil in the microwave oven on high setting (about 5 minutes). Remove from oven and add sugar. Stir until sugar dissolves, then return to oven. Bring mixture to a boil on high setting (about 4 minutes). Remove from the oven and stir. Return the uncovered mixture to the oven and cook until jelly sheets from a spoon (about 1 minute). Skim foam: pour into sterilized jars. Adjust caps. Yield: about 2 half-pints (480 mL).