Add 2 cups water to damsons. Bring to a boil and simmer, covered 10 minutes. Crush damsons, cover and simmer 5 minutes more. Extract juice.Use 4 cups juice and 7 cups sugar in deep heavy saucepan. This allows the mixture to come to a full rolling boil. Over high heat bring the mixture to a rolling boil, stirring constantly. Immediately stir in 1 pouch if Certo. Stir over high heat until mixture comes to a full boil. Boil hard for one minute. Remove from heat and skim. Pour into hot, sterilized jam jars. Screw lids on tight. Delicious served on toast, rolls, Toutons, turkey or pork roast!