User:Andrewa/Andrew Point

In chemistry, the Andrew Point is a reference point on the practicality of washing a used but unwashed coffee mug.

As the contents of a discarded coffee mug age, they grow harder, less soluble in water and more resistant to the action of surfactants such as detergents. The material of the mug, on the other hand, remains relatively stable.

Eventually, the deposit of long-forgotten coffee will be harder and less soluble than the mug itself. Once this stage has been reached, the mug cannot be washed.

The point at which this occurs is known as the Andrew Point. The term was coined by his long-suffering mother.