Executed in 1969, shortly after the Museum of Modern Art's The Responsive Eye exhibition which both formalised the Op movement and cemented its popularity, Marina Apollonio's Dinamica Circolare 9B is a significant work from the artist's most important period.

Created from boldly modern industrial materials, its surface painted with a dynamic black and white geometric sequence for maximum impact and visual accessibility, Dinamica Circolare 9B explores Op's central fascination with perceptual sensation, and the process of participation that activates this sensory experience.

Apollonio's choice of form and decoration are notably striking and therefore inviting, which is important as Dinamica Circolare 9B doesn't rely on any understanding of a conceptual framework to unlock its meaning, it simply requires the viewer to participate in its visual effects. The familiar form of the circle, employed in the present work as in many of her best known creations, and the geometric decoration applied to its surface are immediate in their simplicity and contrast sharply with the complex visual disturbance triggered by the presence of the human eye.

The movement of the alternating tones of black and white is both commanding and inescapable, and forces the viewer to focus entirely on the object in an attempt to make sense of its shifting perspective. This participatory element, so central to Op's investigations into forms of visual communication, is enhanced by the work being mounted on a single pin allowing it to be manually rotated.