By talking of the picture as an improvisation I seem to deny the existence of any preparatory work. In a sense, apart from the choice of the initial panel, there was none. The underpainting of the panels as can be seen is inconsistent and wilfully random: they are provocation rather than preparation.

All painting, since it takes the form of replacing nothing with something, is improvised if only by stealth. So yes, even here a bit of tentative drawing does go on slightly ahead of the brush. I snatch a piece of card that won't soak up oil paint too quickly and rehearse some marks on it. Here is a card currently in use with apologies to the designer bookbinders whose private view invitation it is, or once was.

Another strategy is to print out a photo of the painting in its current state and try out possible next moves on that. This is one I had pinned on my study wall in Princeton: it features also an initial idea of what might happen in the top left hand panel when it was replaced.

These are utilitarian drawings of the kind that, rather than featuring in exhibitions, usually find their way via the studio floor to oblivion.