The beginning of an egg is the tiny ova which takes a week to grow into a proper egg yolk. If you cut a boiled egg in half and look at the yolk, the dark rings were layers made during the day and the light layers during the hours of darkness. Strange but true!
When the yolk is ready it is released along the oviduct. The first part of the oviduct is where the egg white (albumen) is added. The egg white mainly consists of protein, water and minerals.
Then the egg carries on along the oviduct where it grows two connecting strands at the top and the bottom called chalaza, which anchor the yolk to the shell keeping it in the centre of the egg.
The next stage is for the shell membranes to form around the white. After this the egg continues down into the uterus where the shell is added. The shell is made from calcium carbonate, which is also found in marble and chalk. The shell is a great bit of design. It is on average only 0.3mm thick but it is incredibly strong. Duck egg shells are more porous than a chickens egg shell which means that they are more susceptible to taking up the odours of things stored near them such as fish or garlic. They also deteriorate faster so should be used within 2 weeks.
The colour of the shell depends on the breed of duck and on the individual duck itself. Some ducks lay almost black eggs (the Cayuga) and the Aylesbury lays a white egg but the colour of the shell doesn\'t affect the taste.