I heard that people do that to goose eggs.Why would you want to do that? Your only going to cause that water from getting inside that shell, causing either stickiness or possibly drown them.
This is her third yr. And has done great every time. I plan on taking the ducklings as they hatch. So that she will regain she wait so she will go broody twice a this yr.You see you have TWO DOWNFALLS with letting a chicken hatch them
1. if she is a first timer, chances are she is NOT going to sit on those eggs for that amount of time.
2. She may reject them once they are born. My hen looked at my calls and peck the crap out of them, she was like "OH MAN, a deformed hatching". and tried to keep them away from her.
You aren't going to be able to control the humidity, or temp with her. So your best bet is to leave them alone but be prepared, in case she decides to quit or rejects them......
Some hens make GREAT chicken duck mommies..
I am ready. Bring it on!!! HAHA