Clean the jars thoroughly and as instructed above.
Pit the cherries but leave them whole. A cherry pitter will make your life easier.
Place the cherries in the jars leaving about 2.5 cm/ 1 inch of space at the top. Add 1 or 2 tablespoons sugar to each jar (to taste).
Pour water in each jar to completely cover the cherries. Seal the jars.
Take a very wide pot. Place a clean folded kitchen towel inside it. Put so many jars in the pot as they fit, taking care that they don't touch each other. Cover with water and can. Bring the water to a boil and boil the jars for about 15 minutes. Or use a canner.
Take the jars out immediately, place them on kitchen towels, and leave them to cool. Store in a cool, dark place (I keep them in the cellar).
The cherries will keep for a rather long time, the cherries I preserved 2 years ago were still perfect this summer.