The technique used to transfer the cartoon to the ceiling was spolvero, also known in English as pouncing.
In this Renaissance method, the outlines of a full-size preparatory drawing are perforated with many small holes. The pricked cartoon is positioned against the plaster, and powdered charcoal or another pigment is dabbed through the holes. When the cartoon is removed, a dotted outline remains as a guide for painting. The Italian word spolvero comes from polvere, meaning “powder.”
Spolvero should not be confused with buon fresco, which describes painting pigments into wet plaster, or fresco secco, which involves painting on dry plaster. Sgraffito is a different process based on scratching through a surface layer. A related transfer method, incision, traces lines directly into soft plaster with a stylus; artists could use both approaches in practice.
Michelangelo’s ceiling also shows evidence of changing methods. Some areas preserve transfer marks, while others contain energetic direct drawing, revisions, or enlarged designs. That variation reflects the speed and adaptability required by painting a huge vault in daily sections of fresh plaster.