Anything can be art.
When it has become art it is a product.
A product is the end of a process, a waste.
At the same time the start of a new one - food.
Art is excrement, but the waste can be nourishment in another process.
When the piece of art/excrement is sold, a transformation of value occurs that is hard to define. But in that process one might say that the money is the excrement on the concrete level where the value of the art piece/excrement has become more banal, for some even tarnished; something one doesn't like to talk about. But the metaphoric value of art seems to work in a very similar way to that of money.