Candling eggs is the process of holding a strong light above or below an egg to observe the embryo inside. Candling is done in a darkened room or in an area shielded by curtains, and the egg is placed against an aperture and illuminated by the light. Candling allows you to monitor many things including the egg fertility, embryo development, and weight loss rate. Candling also reveals cracks in the eggshells, and eggs with cracked shells should be discarded. Candling can detect bloody whites, blood spots, or meat spots, and enables observation of germ development. Candling can also reveal infertile eggs, which are easy to detect as the egg is clear, and these should be discarded. Candling is a critical skill to develop if you want to incubate your own eggs. Candling does not harm the eggs, and it is safe to take incubating eggs out of the incubator for the few times you will be candling them.