How many years does it take for an egg to turn black?

The process of an egg turning black, such as in the case of a preserved duck egg known as century egg, typically takes several weeks to months, depending on the preservation method used. However, if you are referring to eggs spoiling or decomposing, that can happen in just a few days to a week under improper storage conditions. In general, the specific timeframe can vary based on environmental factors and the type of egg.