This section is from the book "Everywoman's Canning Book", by Mary B. Hughes. Also available from Amazon: Everywomans canning book; the A B C of safe home canning and preserving.
Do not attempt sun cookery unless hot, dry weather is anticipated. Pick berries early in the morning, wash and hull. Allow equal weights of sugar and fruit. Place the berries on platters in a single layer. Make a thick syrup with sugar, adding just enough berry juice or water to dissolve sugar. Pour over the berries in platters. Cover with a piece of plain window glass and set out of doors in the hot sun for a day or two, depending on weather conditions. The glass should not rest on the berries, but should come a few inches from them. When the berries are soft and the syrup has thickened almost to a jelly, it is time to pack them in freshly washed jars. Adjust rubber, cover, and seal lightly. Put in hot water bath, and have water just simmering for ten minutes. Remove from hot water bath and seal.
Pitted cherries, raspberries, and peaches may be sun-cooked in the same way as strawberries.