1. Remove the stalks, wash the damsons, and put into a preserving pan with the water.
2. Cook slowly until the damsons are well broken down.
3. Add the sugar, stir over low heat until dissolved, then bring to the boil and boil rapidly.
4. Remove the stones as they rise to the surface (a stone basket clipped to the side of the pan is useful for holding the stones, and allows any liquid to drip back into the pan).
5. Continue boiling rapidly until setting point is reached. (Test for set after about 10 minutes of rapid boiling.)
6. Remove from the heat, skim, pot, cover, and label.