The development of the embryo within the egg is monitored most commonly by means of candling - shining a bright light through the egg. Candling is difficult if eggs have a very thick or patterned shell.
Eggs may also be tested by Egg Floatation. The egg is placed in a bowl or bucket of water. Fresh eggs will sink, late-incubation eggs will float and live eggs close to incubation can be seen to move.
