Is this a rotten egg?

[pntdhorses]

View attachment 1770001 View attachment 1770002 I’m currently letting my broody hen lay on Mandarin Duck Eggs. I’m guessing this one is rotten and am ready to toss it. It’s very discolored with black markings here and there. No other eggs look like this. Am I correct in assuming that?

 

[Button And Bongo]

I've had eggs like that hatch. Put it under a flashlight or shake it to your ear.

 

[pntdhorses]

I candled it and it doesn’t look like the others. It’s a lot darker. I went ahead and put it under a different broody girl as I don’t want it with the eggs that look good. I guess I’ll wait and see because I would obviously hate to kill the duckling if it’s possibly viable. But it sure looks weird.