- Candling is the process of using a strong light to illuminate the
interior of the egg so you can see the development inside. It is one of those things we do, not
necessarily because we have to, but because it brings the miracle of life right up close. It's fun and
- Candling your eggs is also a good way to find those that
definitely will not hatch early on so they can be removed from the incubator. It's much less traumatic
now, too. Leaving a bad egg in the incubator could cause lots of problems if it explodes. Yes, it could
actually explode leaving a real mess in the incubator not to mention preventing the rest of the batch
from hatching because of bacterial infection.
- You can purchase an egg candler or you can make one very easily.
Either way, the light must be bright and cool.
A few things to keep in mind when you candle your
The heat produced by some bulbs is hot – too much candling
can kill the embryo.
Other than candling at setting
time, day 8 through 10, day 14, and day 18 are the days that would be most
At day 18 you should definitely see development. You can
decide on this day whether to continue incubating the egg in question.
Do not candle on day 19 or after.
To be able to see clearly inside the egg, you should look at the egg at
approximately a 45 degree angle to the light source. You should be able to see the yolk – embryo (at early
stages) and air sac.
Do this in a darkened room or at least with
a dark background so that the sunlight or artificial light is not shining directly on the egg.
As with anything new, the more you
experience this the better you will be able to tell what is really happening. Candling does not hurt the embryo so
this can be done numerous times. Do not do every day though as this will only keep the eggs at a cooler temperature
which will ultimately cause hatching problems because they are being taken out of the incubator too
Below are some examples of what you should
visible yolk in the centre with an air space : This is a freshly
laid unfertilized egg. It is approximately a week old or younger, but it has not been in contact with a
- This egg is only a few days oldand undefined however will probably be
good. The yolk shows up fairly clearly,
and there are no abnormalities.
veins in a yellow mixture: This is a fertilized and developing egg at
about 4 days. This is what you will see for a fertilized egg up until about 10 days. The veins will increase
to a point where the chick's development will actually fill up the space available and cause the shell to
On around day 12 to 16 you can
actually see the chick move!
Opaque, dark mass in shell, unable to
see through: This is a fertilized egg. The chicken growing inside has
blocked light from passing through. This egg should hatch after the prescribed amount of time for the species you
are trying to raise. If it does not, the chick has probably died inside the egg and the egg should be disposed
Opaque, but with a large air bubble off
to one side of the egg: This is an egg that was fertilized, but the
chick has since died. It can be disposed of.
Not opaque, but no yolk, and a large air
pocket: This is an old, unfertilized egg. It can be disposed
Several things to look for which indicate
the dark ring – This egg is no longer viable as the ring is an indication of concentrated bacteria which has
invaded the eggs' membrane. Sometimes all you see is a dark spot which appears in the middle of the yolk area.
Wait a few days and candle again to see if spot has grown and ring begins to appear. If yes, then discard the
The drawing at left shows the development of the air sac as the developing egg loses
moisture. The air sac should be fairly obvious.
This is also a good way to be aware of
humidity in your incubator. If not using a wet bulb thermometer or hygrometer, the air sac gives an indication of
humidity in the incubator. Too little humidity and sac will be larger than it is supposed to be – too much and it
will be smaller.
It is much easier to keep tabs on humidity
with a wet bulb thermometer than to reply on the size of the air sac to gauge humidity readings. The air sac size
is an approximation – the wet bulb will give you a reading. As your experience grows this will become more evident
When candling on days 14 through 16 you
will be able to pretty easily be able to notice the development of each egg. If this is your first time doing this
I would suggest a couple things that might help.
1. Only use a pencil to mark eggs. I use coloured
pencils to mark eggs with potential problems. A marker or pen will seep into the egg shell and very possibly
kill the embryo.
2. Keep a
journal of your progress. Mark all eggs that are possible problems and write this in your journal. Next time
you candle you will remember what the marks mean and which eggs are which!
the eggs carefully sp as not to scramble the contents.
keep them out of the incubator long enough to get the job done. You don’t want to have everything go sour just
when it begins to get exciting.
discard the bad eggs. A rotten egg in the incubator can be a very smelly mess and potentially a hazard to all
the viable eggs in the incubator.
6. Above all – Have