Candling is one of the small pleasures of hatching your own eggs at home. It is the moment you get to peek inside the shell and see whether life is stirring in there. It also happens to be one of the most useful things you can do to protect your hatch, because it lets you pull out eggs that were never going to make it before they turn into a problem in your incubator.
This guide walks you through what candling is, when to do it, and exactly what you should expect to see at each stage. We will keep it practical and honest, because part of hatching eggs is learning to accept that not every egg develops - and that is completely normal.
What Candling Actually Is
Candling simply means shining a bright, focused light through an egg in a dark room so you can see the shadows and structures inside. The name comes from the old days when people literally held eggs up to a candle flame. Today most folks use a small LED candler, a bright flashlight, or even the flashlight on a phone pressed snug against the shell.
The trick is contrast. You want a strong beam of light and a dark room. Cup your hand around the light and the egg to block any leaks, hold the light against the large end where the air cell sits, and let your eyes adjust. Work quickly and gently. Eggs should not be out of the incubator for more than five or ten minutes, and warm hands are better than cold ones.
A few honest cautions: never leave eggs sitting on a hot bulb, do not rotate or shake them to see movement, and always wash your hands first. You are handling living embryos, and they are more fragile than they look.
When to Candle During Incubation
You do not need to candle constantly. In fact, opening the incubator too often does more harm than good. For a standard 21-day chicken hatch, a simple schedule works well.
- On arrival (shipped eggs only): If you ordered hatching eggs through the mail, candle them once when they arrive to check the air cells before you even set them. Shipping is rough, and jostled eggs sometimes have loose, wobbly, or detached air cells. Let those eggs rest large-end-up for 12 to 24 hours before setting.
- Around day 7: This is your first real development check. By now a fertile, healthy egg shows clear signs of life, and you can start identifying eggs that never developed.
- Around day 14: A second check to confirm which embryos are still growing and to remove any that quit along the way.
- Never during lockdown (days 18 to 21): More on this below, but the short version is hands off.
What You See at Each Stage
Knowing what is normal makes candling far less nerve-wracking. Here is roughly what a developing egg looks like as the days go by.
Day 7: This is the magic moment for most beginners. In a developing egg you will see a network of tiny blood vessels spreading out like a spider web or the branches of a tree. At the center sits a small dark spot, the embryo itself, often about the size of a pea. If you are lucky and hold still, you may even catch a little movement or a faint pulsing of the vessels. That web of veins is the sign you are hoping for.
Day 10 to 14: The egg looks noticeably fuller and darker now. The veins are more extensive, the embryo has grown into a larger dark mass, and you will see the air cell at the large end getting bigger as moisture leaves the egg. Less of the egg glows clear because the growing chick is taking up more room.
Late incubation (day 15 to 17): By this point the egg is mostly dark and solid-looking when you candle it, with the air cell clearly outlined at the top. You are seeing shadow, not veins, because the chick nearly fills the shell. Sometimes you will see movement against the light. This is the last comfortable window to candle before you stop entirely.
Telling a Developing Egg From a Clear or a Quitter
This is where candling earns its keep. There are three outcomes you are sorting between.
- Developing egg: Veins, a dark embryo, and increasing darkness over time. Keep it.
- Clear (infertile or never developed): The egg looks exactly like a fresh table egg held up to the light - bright, glowing, and empty except for the shadow of the yolk. No veins, no dark spot, no growth. Either it was never fertile or development never started. A clear egg is a disappointment, but it is not dangerous yet.
- Quitter (started then died): This one began developing and then stopped. The classic sign is a blood ring - a dark red or reddish circle or line that follows the curve of the shell. When an embryo dies early, the blood vessels pull away from it and settle into a ring shape. You may also see a lonely dark blob with no living vein structure around it, or a smeary streak of blood. These eggs have quit.
A blood ring is unmistakable once you have seen one. Instead of the branching, web-like veins of a healthy egg, you get a single clean ring of blood sitting near the shell wall, with nothing growing at the center. It is nature's way of telling you that embryo is no longer viable.
Why You Remove Clears and Quitters
Pulling failed eggs is not just tidying up. An egg that is not developing is slowly going bad in a warm, humid box - the perfect environment for bacteria. Left alone, a rotten egg can leak, smell, or in the worst case build up gas and actually burst, spraying bacteria over every healthy egg around it. That is a fast way to lose a whole hatch.
So when you candle at day 7 and again at day 14, set aside anything that is clearly a clear or a quitter. If you are ever unsure - say an egg looks questionable but you cannot rule it out - it is fine to leave it and check again at the next candling. Just trust your nose too. A genuinely rotten egg often announces itself with a smell, and any egg that looks weepy, stained, or is oozing should come out immediately.
Dark Shells and the Lockdown Rule
Two last practical notes. First, dark brown, olive, and heavily speckled eggs are genuinely harder to candle because the shell blocks so much light. You will need a brighter candler pressed right against the shell, and even then development may be tough to read clearly on the darkest eggs. Do your best, give questionable dark eggs the benefit of the doubt, and lean on that day 14 check. Blue and white shells, by contrast, are lovely and easy to see through.
Second, and this one matters: stop candling once you reach lockdown, days 18 to 21. At lockdown you raise the humidity, stop turning the eggs, and leave the incubator closed so the chicks can position themselves, internally pip into the air cell, and hatch. Opening the lid to candle during this window releases humidity and can cause a chick to get shrink-wrapped in a dried membrane. Whatever you did not catch by day 17, you leave alone. Set the eggs, trust the process, and let them cook.
Candling gets easier every single time you do it, and before long you will read an egg at a glance. Here at Raptor Ridge Homestead in Bradford, Vermont, we candle every batch of our heritage hatching eggs and we are always happy to talk hatching with the folks who order from us - just reach out at [email protected]. Happy hatching.
