I made the flames lick the surface of the painting in such a way that is recorded the spontaneous traces of the fire. But what is it that provokes in me this pursuit of the impression of fire? Why must I search for its traces? Because every work of creation, quite apart from its cosmic position, is the representation of pure phenomenology – every phenomenon manifests itself of its own accord. This manifestation is always distinct from form, and is the essence of the immediate, the trace of the immediate.

In 1961; p. 67 - "Yves Klein, 1928 – 1962, Selected Writings"