This section is from the book "Preserving And Pickling", by Mary M. Wright. Also available from Amazon: Preserving and Pickling: Two Hundred Recipes for Preserves, Jellies, Jams, Marmalades, Pickles, Relishes and Other Good Things.
In choosing currants for jelly select those that are barely ripe. Pick out leaves and poor fruit, and wash and drain. It will not be necessary to stem them. Just add enough water to prevent them from burning, and heat slowly. Mash the berries, but do not let them come to a boil. Pour into jelly bag, and allow juice to drain or drip into a vessel, without squeezing, if you wish a clear red jelly. Use granulated sugar, a pound to each pint of juice. Place the juice in a preserving kettle, and when it comes to a boil add the sugar that has been heated in the oven.
This jelly will be ready to pour into the glasses five or six minutes after the sugar is added, if none or little water has been added; but it should be tested before removing from the fire. Currant juice, combined with red raspberry, rhubarb, gooseberry, and other fruit juices, will give you a variety.
Gooseberries used for jelly should be green, and will require about a fourth cup more sugar to each pint of juice than the currants. Prepare the gooseberries as you would currants.