In contrast, a good bird can be shown over a considerable period of time with more or less consistent results. I do not say that i never show eggs twice. In the summer, if two shows are close together, I will use the same eggs and in the winter, the same eggs could be shown over a two week period without too much deterioration taking place.
Deterioration is due mainly to evaporation.
The rate of evaporation is affected by the area of shell surface to volume of the contents. Certain egg shapes lose water quicker than others. External conditions too, affect the water loss. For example, eggs stored in a warm, dry environment will age faster than those kept in cool, humid conditions. It is well known that eggs will keep longer in a refridgerator and if thid also contains a dish of water, little evaporation will occur at all.