In other years I have tried preserving quinces many ways. The traditional bottling methods I have found to be incredibly difficult and time consuming. Even then often the quince cores are rock solid.
This year by shear chance I came across my new and permanent method. No more trying to peel rock solid quinces or decore them.
Now I quarter the quinces, take a full slice out that removes the core section, put them in a single layer and only just cover with water. They go in the bottom of the oven with whatever else I am cooking and whatever temp. I leave them in the oven when it is cooling. Make a sugar syrup of 3 parts water to 1 part sugar and boil well. Remove hotish quinces from the oven, the skin just peels off. Put them into sterilised jars, top up with sugar syrup and seal. Sooo easy.