Wash and drain the cherries well.  Place them on absorbent kitchen paper and let dry.  Stone the fruit over the preserving pan, so no juice is wasted.  The stoning should be done with a cherry stoner, if available.  Reserve the kernels in a bowl of water.

Having stoned all the cherries, cover them with the sugar and add the water in which the kernels were soaking.  Allow to stand overnight.

Bring the cherries to a boil and cook until the juices thicken, removing with a slotted spoon any scum that appears.  Just before end of cooking time, add the lemon juice or citric acid.

Remove the pan from the heat, and allow to cool. While they are cooling, grasp and shake and twirl the pan  several times, to stir the preserves. This will allow the fruit to soak up more liquid and to swell up more.