Schiffermüller included 12 colors in his circle, referring to Castel's ideas of color-sound correspondences. Vignettes surrounding the color wheel suggest its applications in painting and connections to the sciences.Upper left, two putti are discussing the rainbow; upper right, one is explaining to the other, as a third draws a rainbow refracted onto a wall through the fountain at center. Lower left: a putto recreates Newton's prism experiment; lower right: a putto paints a rainbow, upon which a figure (God?) sits, over a land and cityscape. Source: From Ignaz Schiffermüller, Versuch eines Farbensystems (Vienna, 1772), plate I.