* unprimed canvas as the ground to imply the lack of an intentional ground?
* primed or very lightly ainted works as a contrast to the figure which is thickly painted (or very worked)
* the significance of nothingness as a background...
is it unimportant or super-important?
In one viewpoint it could mean that the nothingness is merely neglect or disregard for what would be there in traditional pictorial space because it is not important or relevant to the content of the picture; sometimes a concious removal to be sure that there are fewer distraction.
Another perspective is that the nothingess, by stark contrast to the rest of the picture, stands out and becomes the most important part of the work.
Speaking less abstractly, in the wave paintings, the wave can be the most important element, thus making it a symbol/sign,so it is all that is needed (no need to place it in some kind of pictorial context). Or the unworked blank space could be the nothingness or mysterious unknown, just like when in the trough of a big wave, and you getg a glimpse of the sky, but not any grounding reference points. Same can be said for a horizon line; on the ocean or on a river. What is beyond the horizon? Something? Nothing? Difficult to tell when you can't see it.