Helen Pashgian’s Untitled (Light Green Sphere) (1970) embodies her pioneering investigation into light, colour, transparency and perception. Working with cast polyester resin and formed acrylic, Pashgian uses the inherent optical qualities of these materials to create a work in which light appears to move through and become embedded within the form. The choice of the sphere is central to this effect. With no beginning or end, front or back, the perfectly continuous form has a sense of physical completeness, yet its transparency and internal reflections make it appear almost weightless and internally illuminated.