What does a dud egg look like? Can it be dark all the way through apart from air bubble? I have several broody hens and when I went away for a long weekend three weeks ago, they started sitting on eggs. I let them have them for a few days before candling them. Of six eggs, one showed obvious veining, and the others were clear with floating yolks. I put the fertilized egg under one broody and gave the other broodies the non-fertilized eggs to keep them happy and prevent them from fighting over the viable egg. I've candled the one egg a few times and seen development. We're now at between 19-21days depending on when they were layed, and I candled one final time. The egg shows a lot of veining still and some clear areas so I think its on the young side still, but it does have very large air bubble. I then candled a few of the dud eggs to compare bubble sizes. Most were clear with floaty yolk, but one was very dark with the bright air bubble! The air bubble seemed to move a bit changing from round to saddle shape and I could barely see some stuff flowing around within the dark area as I tipped it. Can dud eggs go dark as bacteria grows? It doesn't smell any different than the others.