Press the pulp out of each grape. Boil the pulps until tender, then pass them through a colander to remove the seeds. Mix the skins with the pulp and juice, add as many cupfuls of sugar as there are of grapes, and boil all together until well thickened.
Seal while hot the same as other preserves.
Green grapes are preserved by cutting each grape in halves, taking out the seeds, then adding an equal quantity of sugar, and boiling all together until of the right consistency.