Soak sliced pears in a bowl of water with a bit of lemon juice or citric acid to prevent browning. Drain.
Measure sliced pears and add 1 part sugar to 2 parts pears.
Combine pears with sugar in a stainless steel pot, cover and let them macerate overnight.
Stir in lemon slices and other spices, if desired, to the pears.
Bring mixture to a high simmer or low boil over medium heat. The higher the temperature, the more frequently it will need to be stirred. A large batch usually takes at least 2 ½ – 3 hours, but if the simmer is too low, it can take 4 hours to cook.
Stir occasionally and check for desired consistency after 1 ½ hours. Stir and check them every 15-20 minutes. The preserves are finished when the pears have turned rose color, then to light garnet color and are transparent.
Store preserves in the refrigerator or they can be processed in a water bath canner.
If canning, sterilize jars and have them ready and hot, resting in a water bath canner.
When the preserves are done, ladle the pears into hot jars. Process jars for 10 minutes.
Let jars rest for 24 hours after canning and check the seal.