If you have a small flashlight that has a lot of lumens, use that. I have a nice 200 lumens flashlight I got at Walmart that can see through even black copper marans eggs. I love the thing. Good luck and don't give up hope! With broodies I've found they almost always hatch on day 21 and not any sooner, and sometimes later, since they are getting off the nest, while most of us aren't cooling the eggs in our incubators.
My small flashlight doesn't have batteries currently. I've been using a larger one.
Nothing happened as of yet, but I went out and tried to candle. Only one I could see through was the older, paler Marans egg--wasn't good. But, I held other eggs up to my ear, and I'm pretty sure I heard one tapping! No chirping though. I thought I would only hear tapping after they are through the air cell and can touch the shell. So why no noise? Maybe I was imagining things...I'm starting to doubt myself...