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Candling incubated chicken eggs: the fascination of watching a speck grow into a chick.

Candling chickens eggs: what it means and how to do it. Pin for later.

Candling your eggs as the embryo develops is one of the most exciting parts of incubating and hatching your own chicks.

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If you're not sure what candling means or how to do it, you're in the right place.

This article gives you the low-down on everything you need to know:

* What does candling an egg mean?

* How is it done?

* What problems might there be?

* What should you be looking for?

Finally, I answer some of your most often asked questions about the candling process.

Let's start at the beginning.


This is a lengthy, very detailed page. Use these links if you want to reach a particular section quickly.


What does candling chicken eggs mean?

Put simply, candling is the name given to looking at the inside of a developing egg by shining a bright light through it. 

It's used by people who are incubating chicken eggs (or any other kind of egg) for two reasons:

Candling gives valuable clues as to whether you should expect problems during incubation - whether the embryo has died, for example - or after hatch. It's a critical skill to develop if you want to incubate your own eggs.

In this article, you'll learn all you need to know to become a competent candler.


How to candle.

It's really very simple.

  • Always wash your hands before candling, to avoid transmitting any bacteria onto the egg. As the egg gets further into incubation it becomes more porous, and the last thing you want is a warm, humid incubator full of bacteria.
  • Candle on a soft surface. I usually use a towel. If the egg accidentally drops, which isn't unknown, it has less chance of smashing than if it fell onto, for example, a wooden table.
  • Try to candle when it's quiet and you'll be undisturbed. If you have children who want to watch, make sure they know to avoid sudden movements.
  • You'll need to turn the room light off, so it's a good idea to have a torch available if the switch is any distance from the candling table.
  • Take an egg from the incubator one at a time. Try to do this when your incubator is having its "cool down" time. 
  • Always candle with the pointed end facing downwards. Avoid jolting the egg - be very gentle.
  • Keep the eggs outside the incubator only for as long as it takes to candle them.

Candling eggs at day 5 of incubation - a video.

In this video, I use Brinsea's candler and OvaScope to candle some eggs at day 5 of incubation. Look for...

  • The "spider" of embryo plus veins which tell us the egg is fertile
  • The air cell, which tells us the chick is growing well
  • Any cracks in the shell which might become a problem.

When to candle.

  • Candling before your eggs go into the incubator is always a good idea. To find out why, have a look at this page.
  • Once they are set in the incubator it's not a good idea to candle every day, even though it's very tempting. If you've got children they will probably want to because it's an exciting process. But accidents can happen, no matter how careful you are, so try to limit it. 
  • Candling somewhere between Day 5 and Day 7 is a good idea to see which eggs are developing. At that stage, mark those that don't seem to have developed.
  • At Day 10 re-candle those you've marked as possibly not being viable and, if they still show no signs of developing take them out of the incubator. It's hard, but it has to be done.
  • At Day 17, just before 'lock-down', candle all your eggs to make sure none have died in the meantime. If any are showing signs of non-development take them out of the incubator now.
  • Leaving those which have not developed, or started but failed to continue, can cause them to explode and scatter bacteria over the rest of the incubator. That's a real no-no if you want a successful hatch because bacteria can enter the other shells and kill the embryos.

Different types of candlers.

Using a candle to candle eggs.

Candling chicken eggs used to be done using a naked flame.

Talk to older people who hatch their own chicks and they'll tell you it's called "candling" because it used to be done with a candle.

The incubated egg was held over the flame in a darkened room, which allowed the person to see through the shell. 

Perfect? No, not at all.

The problem with using a candle is that they're unstable - and very hot. The last thing you want to do with a fertile egg is cook it.

So candles had their drawbacks and should never be used in modern hatching.


Using a flashlight as an egg candler.

Hand-held candlers are efficient but hard to hold with an egg balanced on top!

Definitely a step in the right direction, flashlights are not as hot, and a lot more stable.

Even now it's easy to use a small flashlight for candling. You just need a strong light - halogen bulbs are ideal - and either a home-made box or your hand, made into a fist. 

Dealing with the fist-version first, it works by the light being held inside the fist with the bulb close to the top and the egg balanced on the clenched fist. 

The benefits of this are that it's a relatively cheap way of doing it, and it's very simple.

Drawbacks? The light tends to be less strong because some of it is absorbed by the hand.

But the main drawback is potential accidents. It's very easy to drop an egg balanced on a fist, especially if you're trying to take photographs at the same time.

Make sure you candle on a soft surface in case you drop the egg. I use a towel on my candling table.

If you'd like to use a flashlight, make sure it has a strong, preferably, LED, lamp. This little light, which is also inexpensive, is ideal.


DIY egg candlers.

  • A second option for this hand-held method is a flashlight app on a smartphone.
  • I occasionally use this if I want to candle an egg quickly and don't have time to set up my ovascope. As long as you have a strong light, it works reasonably well.
  • I've also used an inexpensive LED light I bought at a supermarket, with a round cardboard ring which I taped on to concentrate light into the egg.
My home made LED light candler.
  • Although the light was bright enough, I couldn't prevent it from spilling outside the cardboard ring even using duct tape. So sadly, it wasn't very effective.

The home made box candler.

If you're not sure whether you're going to hatch again (although I guarantee you will!), you may not want to invest in a commercially-made candler

A home-made, table-top candler isn't difficult to achieve and can be very effective. Have a look at this short video which shows how it can be done.

  • Advantages of a home made candler: It's cheap to make and very effective.
  • Disadvantages: You need to be very sure the heat doesn't build up. You don't want to cook the eggs.
  • Because it doesn't enclose the egg, dark shells such as the chocolate brown Marans are very difficult to candle, even in a darkened room.

Commercially made candlers.

This is the modern equivalent of both the candle and the flashlight - and much easier to use.

Powered by batteries, this high intensity candler's light is not hot, but is strong enough to give an excellent view through the shell, especially if used in a darkened room.

Use it with an 'ovascope' and you have the perfect combination.

  • Advantages: Very easy to use and, when combined with the ovascope (the black contraption above which looks like a microscope), they're particularly good for candling dark shells like the Marans.
  • Wonderful for children to be able to see the developing chick - brings alive the wonder of birth as if by magic.
  • Disadvantages: Quite expensive to buy, particularly if you're not sure you'll hatch chicks frequently.
  • For my detailed review of the Brinsea candlers and the OvaScope, including pictures showing how they work, see this page.

Frequently Asked Questions.

Why is candling important?

For four reasons:

  • To analyse problems if you have a poor hatch rate.


Will candling tell me whether an egg is fertile or not before incubation?

No. 

The only way of knowing whether it's fertile - short of breaking the shell open - is by incubating it for six or seven days. If you candle then, a fertile egg will have a small embryo forming together with some spider-like veins.  

This is one of my Wyandotte eggs at Day 5 of incubation. You can just begin to see the tiny dot of the embryo in the middle, with veins running off to the side.

A candled egg at day 5.


How do I know what I'm looking for?

  • You're watching for proper development of the egg, and any cracks or blood rings appearing.
  • If you're new to candling, you'll need help to gauge whether what you're seeing is what you should be seeing.
  • My step-by-step guide to hatching covers exactly that with text, photos and video-clips. You can find out more about it here.


Does it matter which way up the egg is when candling?

It's wise to keep the more pointed end of the egg facing down. I very occasionally candle with the blunt end down to be able to see the embryo more clearly, but it does run the danger of damaging the embryo, particularly in the first couple of weeks.

Please note: fertile eggs should always be stored and incubated with their more pointed end downwards.


Does moving the egg during candling damage it?

No, as long as you're careful and as long as you don't candle after day 18 of incubation. You will generally need to turn it to see what's going on inside, particularly as you come to the later stages of incubation. Always take it slowly.

Commercially-made ovascopes like the Brinsea have a turning wheel to help with this. If you don't have an Ovascope, use your hand to turn but be careful - eggs slip easily. 


How long should the egg be out of the incubator?

As little time as possible. If you're just checking whether it's damaged or developing, candling should only take a few minutes. If you've got children who are keen to see what's going on inside, it may take longer.

As a 'rule of thumb', you shouldn't keep it out of the incubator for longer than thirty minutes absolute maximum. I try to candle when the incubator is cooling down for an hour each day, as both the Brinsea incubators I use do.


Is it safe to mark eggs during candling?

Marking an incubated egg to show development.Marking air cell development at days 10 and 15. The check mark tells me this egg was fertile at day 5.

Yes, it's perfectly safe to mark eggs as you candle them, and it helps keep an eye on progress. 

  • Using a pencil (don't use a marker pen - the ink can infiltrate the shell), mark the day it was candled together with whatever your 'shorthand' is for "developing", "not developing" or "not sure".  
  • It also helps to mark the air cell at intervals so you can see that it's still growing, particularly during the final stages when it's hard to see much else. 
  • This will tell you, once the chick starts to 'pip' - break through the shell - whether it's in the right place or not.
  • I also mark each one with its breed and with a number which I then keep on a chart. 
  • This allows me to keep tracks on which eggs have been most successful and to look at possible areas where I can improve the likelihood of a good hatch.

Keen to candle but not sure what to look for? 

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My hatching course takes you step by step all the way through the process of incubation and hatching. It assumes no knowledge and looks at the first steps of deciding whether hatching your own is a good thing for you, to choosing the right eggs, what to expect at each day of incubation and the highs and lows of hatching.

The course is suspended for this year (2020) due to lack of eggs owing to the Coronavirus, but will resume as soon as possible.

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Like to know more about incubating and raising your own chicks?

Incubating equipment explained - link.
How to choose the best chicken eggs for incubation - link.
Preparing fertile eggs for a successful hatch - link.
Incubating chicken eggs - an overview. Link.
What do baby chicks eat? Link.
Link to Raising Happy Chickens home page.