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

This page is part of my step-by-step guide to incubating, hatching and brooding chicks. 

To find out more, click here.

Chicken egg being candled.

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

But not everyone knows how it's done or even what it means.  I certainly didn't when I first started out!

So I've written this article to give you the low-down on everything you need to know about what candling means:

  • how it's done,
  • the problems you may come across and
  • what you should be looking for.

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

Let's start at the beginning. What exactly is candling?

In a nutshell, 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: firstly to test whether an egg is good enough quality to go into the incubator, and then at different stages during incubation to see whether the embryo is developing as it should.

Candling gives valuable clues as to whether you should expect problems during incubation 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.

The history of candling.

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

Talk to older people who used to incubate and they'll tell you it's called candling because it used to be done with - well, with a candle.

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

Perfect?  No, not really.

The problem with using a candle is that they tend to be unstable - and very hot.  The last thing you want to do with a fertile egg is cook it.  So candles had their drawbacks.

Enter the flashlight!

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

Definitely a step in the right direction, flashlights were 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 main one is that it's very easy to drop an egg balanced on a fist, especially if you're trying to take photographs at the same time.  The light also tends to be less strong because some of it is absorbed by the hand.

 What about 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 money in a commercially-made candler. 

A home-made candler isn't difficult to achieve and can be very effective.  Have a look at this short video to give you an idea of how it can be done.

  • Advantages of a home made candler : It's cheap to make and very effective.
  • Disadvantages : Because it doesn't enclose the egg, dark shells such as the chocolate brown Marans are very difficult to see inside - even in a darkened room.

Then there were the commercially made candlers.

This is the modern equivalent of both the candle and the flashlight and is very easy to use.  Powered by batteries, its 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.

My Brinsea ovascope and candler.
My Brinsea candler and ovascope - I love them! Available to purchase from
  • 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.
  • They're 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're going to be hatching chicks frequently.
  • For my detailed review of the Brinsea candlers and the OvaScope, including pictures showing how they work, see this page.

How to candle: Frequently asked Questions.

Why is candling important?

For four reasons:

  • To make sure the eggs are the best possible quality before they go into the incubator
  • To watch the embryo develop during the 21 days of incubation
  • To help know to discard eggs which are not developing before they explode and spread bacteria through the incubator
  • To analyse problems if you have a poor hatch rate.

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

Afraid not. 

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 Wyandottes 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, showing an embryo and blood supply.

How often should I 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 - and 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 it can enter the other shells and kill the embryos.

How is candling done?

Candling eggs in the daylight won't work - find a darkened room.Candling in daylight won't work - you need to find a darkened room, or use an Ovascope.

It really isn't difficult.  Particularly if you're new to candling, it's a good idea to use a soft surface so that, if you do drop one, it has a better chance of surviving.  I use a folded towel.

It should be done in a darkened room, otherwise you won't be able to see anything very clearly.

Place whichever candler you're using on the surface and turn it on.  Carefully take the egg from the incubator and stand it on top of the light.  If necessary, cup your hand behind it to help you see better.

How do I know what I'm looking for?

If you're new to candling, you will 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, images and video-clips.  You can find out more about it here.

Does it matter which way up the egg is when I candle?

Not really.  Fertile eggs should always be stored with their more pointed end downwards and you can begin candling in the same position.  However, if you can't see clearly it can sometimes help to turn it the other way up.  

Does moving the egg when I candle 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.

Commercially-made ovascopes like the Brinsea have a turning wheel to help with this; otherwise just use your hand 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, as it does each day.

Is it safe to mark eggs during candling?

Marking an incubated egg to show development.Marking to show air cell development at days 10 and 15. The check mark is my 'shorthand' for 'fertile' when first candled.

Yes, it's perfectly safe to mark eggs as you candle them, and I find it helps with keeping 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? 

Candling is a really fascinating experience, but it helps to know what you're looking for.

My free, day-by-day guide to incubating, candling and hatching your own eggs gives you exactly that.

To find out more, have a look at this page, or fill out the simple form below to get free emails delivered straight to your inbox with step-by-step guide.

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

These pages have been written with the first-timer in mind but have enough information to keep more experienced hatch-a-holics happy too.

Click on any of the links to go to that page.

How to choose eggs with the best chance of hatching - link.
Link to a detailed review of my favourite incubator : the Brinsea Mini Advance.
What happens on the first day of incubation? Find out at this link!

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