I used to love to do this when I was little. Dad rigged up a light 
bulb inside of a round cardboard vodka box (I think), with a small 
hole in the top to set the egg to candle. I remember seeing the baby 
bird moving or not moving and taking any of the ones that were dead 
or non-viable eggs (which were few) out of the incubator.

Eggs are candled to determine the condition of the air cell, yolk, 
and white. Candling detects bloody whites, blood spots, or meat 
spots, and enables observation of germ development. Candling is done 
in a darkened room with the egg held before a light. The light 
penetrates the egg and makes it possible to observe the inside of 
the egg. 
The candler should be set on a box or table at a convenient height 
(about 38 to 44 inches from the floor), so the light will not shine 
directly into the eyes of the operator. In candling, the egg is held 
in a slanting position with the large end against the hole in the 
candler. The egg is grasped by the small end and, while held between 
the thumb and tips of the first two fingers, is turned quickly to 
the right or left. This moves the contents of the egg and throws the 
yolk nearer the shell. Because of the color of their shells, brown 
eggs are more difficult to candle than white eggs. 

To do a reasonable job, an extensive knowledge of candling is not 
necessary, particularly if the eggs are all relatively fresh. One 
should be able to distinguish a fresh egg from a stale egg and 
detect such abnormalities as bloody whites, blood spots, meat spots, 
and cracked shells. In a fresh egg, the air space is plainly visible 
and moves freely. The white is thin and clear. In a stale egg, the 
air space is plainly visible and moves freely. The white is thin. 

Most newly laid eggs are good quality. Eggs not over two or three 
days old, if held under good conditions, will meet the 
specifications for Grade A. The only eggs to be removed by candling 
are those with bloody whites, blood or meat spots, and cracked 
shells. 

Incubated eggs are candled to determine whether they are fertile 
and, if fertile, to check the growth and development of the embryo. 
White eggs should be tested for fertility on the third day. Brown 
shelled eggs on the fifth or sixth day because it is difficult to 
see the embryo clearly before this time. 
A small reddish area with blood vessels extending away from it will 
be visible in fertile eggs. This is the embryo floating around 
inside the egg, looking like a huge red spider. If the embryo dies, 
the blood draws away from the embryo and forms what is called a 
blood ring. All clear eggs and eggs showing blood rings or streaks 
should be removed from the incubator. If eggs are not candled during 
the early stages of incubation, it will be difficult to determine 
whether the egg was fertile; embryos that die early soon decompose 
and are not easily distinguished from rotten eggs. 

Candle the eggs every few days to observe the growth and development 
of the embryo. Record findings to learn from.

tenzicut

