How know a lot about ducks and can help me with my questions?

How can you make a makeshift incubator for duck eggs. I have tried putting some duck eggs in a box with some papertiles and a hot water bottle. I wonder will that help incubate the eggs. Also about how long can a mother duck stay off her eggs after she lays them. I have shined a flash light over the eggs but all i can see is liquid and one of the eggs have cracked open and all I say was a yellow liquid. Does this mean that the egg is not fertile or rotten.