Pare the quinces, cut in quarters and remove the cores and woody portion beneath. Cook the cores and skins with water to cover about an hour, then strain off this water and in it cook the quinces and half as many sweet apples, also pared and cored, until each is tender or can be pierced with a straw. Let the fruit stand in cold water after preparation until time of cooking. Cook only as much fruit at a time as can be covered by the liquid. Remove with a skimmer when tender. When all the fruit has been cooked, add to the liquid a pound of sugar for each pound of quince and half a pound of sugar for each pound of apple; boil five minutes, skim and add the fruit and let cook slowly until of the desired color; long cooking gives a dark-tinted preserve. Drain on a platter and when all are cooked and drained, store in jars, straining the hot syrup over the fruit. Use only the liquid from the cores and skins that drains through the cloth. It is often best to discard the cores as they contain gummy properties detrimental to the jelly.