I am completely new at chick hatching but I've kept chickens for years. I want to candle correctly and understand what I'm looking at. To cut to the chase, 9 out of 11 28 day old eggs were "clear", "transparent" with no veins or blood. I have three that you can't candle through. They are opaque and may not be that old. What does a "black opaque" egg indicate? Thanks