What is White?

Although built on a dark gray ground, the series of paintings for White was conceived of as a process of layering white on white, using a range of viscosities of paint. "What is white?" is a question I pose when teaching color relatively in my Fundamentals of Two Dimensional Art course. Students paint an achromatic chart in which they begin with black and, therefore, can only achieve optical white, not pure white. The lightest value on the chart appears white, but when I have them compare it to white, they can see it's gray. So, what is white? Snow white? Oyster white? Cool white? Warm white? The Sherman Williams paint chart lists approximately twenty whites. If you're wearing a white shirt and you look at the folds, is the material that's not in direct light still white even though it appears gray? It is this inquiry that is the basis for my series of white paintings. Most of the paintings are titled with the name of a commercial white paint.