Squeeze juice from oranges. Tie pips in a muslin bag. Cut oranges in thick shreds. In a large saucepan, simmer orange and orange juice, shredded oranges, muslin bag and water 2 hours or until orange peel is soft. Discard muslin bag. Add sugar and treacle and stir until sugar dissolves. Increse heat; boil rapidly 15-20 minutes or until marmalade reaches 105C.
Fill into hot jars and seal.