A photograph printed once, on baryta or rag satin paper, then crumpled or folded and scanned again. It's the passage of the scanning lamp that produces this fire-like blistering of light, as it clashes in the hollows of the satin-finished paper.
A double action of light: the first when it burns the film during the shooting (the film is exposed to light to produce the photograph), the second when it scans the surface of the print, which is supposed to be flat, revealing a second collision with the material.