Candling gets its name from days gone by when people used to use candles as the light source to view the contents of eggs.
Today you can purchase candling torchs for your needs.
"Candling" is the term used to describe a method by which bird breeders check to see if eggs are fertile or not.
When an egg is candled, a bright light is held at the base of the egg, to illuminate the shape and the contents in the shell.
The breeder can then determine whether or not the egg is fertile based on the color, shape, and opacity of the contents.
" Fertile Egg!"