Measure currants into a preserving kettle.
Add an equal quantity of water.
Cover and simmer until the fruit is soft (10-15 minutes).
Crush periodically with a potato masher.
Pour into a jelly bag and let the juice drain out overnight.
Measure out 4 cups of the juice.
Place in preserving kettle.
Bring to the boil.
Boil 3 minutes.
Add 4 cups sugar.
Return to the boil and continue cooking over high heat until the jelly sheets, about 5 minutes.
Remove from the heat immediately.
Rest 1 minute.
Skim with a metal spoon.
Pour into sterilized jars.