This series of drawings, made on special paper that was previously smoked, is one of Moreno Villa’s most curious and surprising works. They demanded a complex and laborious preparation of the medium, and immediacy in their execution, for they cannot be corrected. The grafumos were a “whim” in Moreno Villa’s artwork, both for their uniqueness and their scarcity.

As he told a Mexican journalist in 1947: "When he was in the laboratory of Physiology [of the Residencia de Estudiantes], looking at the graphical line drawn by the heart beat of a rabbit having surgery, he felt the need to get those crisp white papers that cardiologists use, make them smoky, and draw on them. And the professor, who, incidentally, was Dr. Negrín, put at his disposal the place, the paper, and everything he needed.”