So our pekin has been sitting full time for about 4/5 days on 15 eggs. My partner decided to candle them today and mentioned that some of them are going dark? I came in and had a look myself, and its really hard to explain what it looks like.. I'm assuming the air sac is the white circle at the bigger end of the egg? that looks fine. but where im assuming the yolk was its like someones cut out a square of dark paper and stuck it to the inside, it doesnt go all the way around so theres a gap on the opposite side which is completely clear. I couldnt spot any veins in the dark but but it was hard to see properly because its the middle of the day and by the time i came back with a toilet roll and a better torch she'd jumped back on the nest. Two eggs looked like this, and im just wondering if they've gone bad and if i should throw them away or leave them a bit longer or check them again when its dark and take a picture to show you what I mean.