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 making this preserve use two-thirds quinces, and one-third sweet or semi-sweet apples. Pare and quarter the fruit, and core, removing all hard parts; then slice into thin slices. Cover the quinces with cold water and simmer until tender, then remove with a strainer, and add the sweet apples to the water that remains, adding a little more water if necessary. Cook the apples until tender, then remove with a strainer.
Boil the juice for several minutes before adding the sugar. Allow three-quarters of a pound of sugar to each pound of fruit. After the sugar is in, boil until the syrup is thick, then add the fruit, and cook until clear and of the right consistency for preserves. The fruit should not be stirred, but kept as unbroken as possible. Fill into preserve jars and seal This makes a delicious preserve.