Wash the quinces and rub off any fluff from the skins.
Peel and core the quinces, retaining the skins and cores (see note below).
Cut each quince into eight pieces and place them in a pan.
Cover with water and add the salt, then bring to the boil.
Simmer for about 10 minutes, then strain the liquid from the fruit, and retain both the liquid and the fruit.
Return the fruit to the pan.
Measure the cooking liquid into another pan, and for every 600 ml (1 pint), add 450g (1 lb) sugar, 150 ml (1/4 pint) vinegar, 1 teaspoon coriander seeds and 1/2 teaspoon cumin seeds, both of which have been gently roasted in a frying pan.
Bring to the boil over a medium heat, stirring until the sugar has dissolved, and then simmer for 5 minutes.
Pour the liquor over the quinces and bring to the boil.
Simmer gently for 45 minutes.
Using a slotted spoon, transfer the quince pieces to warm, sterilised jars.
Continue cooking the liquor for a further 10 minutes, until you have a syrup that covers the back of a spoon.
Pour the syrup over the quince pieces and seal the jars.
Allow the pickle to sit for a month before using.
Store in a cool, dark place.
Adapted from Spiced Quinces "Good Old-Fashioned Jams, Preserves and Chutneys", 2008, Sara Paston-Williams, National Trust Books, p60.