One of my favourite tasks on the farm is candling and sorting the eggs. When I hold the bright light up against the eggs they glow like old fashioned Christmas lights. With the green eggs I can see the yellow of the yolk through the shell, on others it shows as a faint shadow and on some I can barely see it at all. Sometimes I can make out the tiny air sac at one end – if I want to boil eggs I keep them for a couple of weeks and then candle them again to see if the air sac is big enough to let the shell come off cleanly. You can do this yourself with a bright flashlight – the small LED ones are great as long as the batteries have a good charge. All you need to do is turn out the lights – the darker the room the better for this – and hold the flashlight against the egg so that no light escapes around the egg (this is why the small flashlights are best).
I had intended to include pictures of the candled eggs but I haven’t quite worked out how to take a good photograph of them.