Pare and core ripe quinces. Cut them up and weigh them. Put the quinces over the heat with 1 pint of water to each pound of fruit and allow to simmer, but not long enough to change the color to red - it should be quite pale. Strain through a jelly-bag. Weigh the juice the next day and place in a large saucepan. Boil quickly for 15 minutes, then remove from heat and stir in 12 oz of sugar for each lb of juice. Boil for another 15 to 20 minutes, till cooked, stirring all the time. Remove the scum.