Separate pulp from skins of grapes. If desired, chop skins in a food processor.
Cook skins gently 15 to 20 minutes, adding only enough water to prevent sticking, about 1/2 cup.
Cook pulp without water until soft. Press through a sieve to remove the seeds. A food mill also works well.
Combine pulp, skins and sugar. Slowly bring to a boil, stirring occasionally until sugar dissolves. Cook rapidly almost to jellying point (220 degrees), about 10-15 minutes.
As mixture thickens, stir frequently to prevent sticking. Pour the boiling hot mixture into hot jars, leaving 1/4 inch head space. Adjust caps. Process for 15 minutes in boiling water bath.
Yield: about 3 pints.