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.
Currants are good sun-preserved. For this purpose use only the most perfect berries, pick over carefully and wash. The large cherry currants are best preserved in this manner. Use two-thirds of a pound of sugar to each pound of fruit. Spread the currants on platters, and cover with sugar, and allow to stand overnight; then in the morning place the platters in the oven a few minutes to melt the sugar and extract the juice not brought out by the sugar.
Then place the platters in the sun in the hottest place you can find; they should be placed on light tables or stands so that they can be easily moved about as the sun changes. Cover with double mosquito netting to keep out the flies and other insects, placing something higher around the platters to keep the netting from getting down into the fruit. In two or three days the syrup about them will thicken up, and the fruit become semi-transparent. The time will depend on the intensity of the sun.
They are now ready to pack away in jars. Self-sealing jars are excellent for this purpose. Place some granulated sugar over the top, then pour over this melted paraffin and screw on the lids.