A very powerful candler and a dark room. I have the same trouble with penedesenca eggs. I don't even try.
When we were incubating out welsummer eggs which are very dark we couldn't see in well enough with a flashlight so we borrowed my mother in law's slide projector, it worked GREAT with the dark eggs!!! Don't know if you have one or know someone who you could borrow one from but that's the only thing we could come up with. Good luck!
Hi StoneFamily, I was also having trouble seeing into my eggs so I built a second candler and have light at both ends of the egg. I will try to take a picture of them side by side. I use a 13 watt flourescent bulb in a small box for one side and a maglite through a 3 cm tube on the other side. (Both are cool sources of bright light.) It really illuminates well and has the added benefit of "holding" the egg in between while your fingers carefully turn to see all sides of the egg. -The photo shows a 'clear', (infertile) egg from my RIR.
Use a bright light, one good enough to see white eggs with excellent clarity of the life and veins inside. Candle from the blunt side, and around day 7-14 if you see nothing at all but a bright aircell on that end, you're good. If the entire egg glows red during that time, it's very likely a dud.
