Nicholas Spice reviews a retrospective exhibition of works by painter Agnes Martin, on view at Tate Modern through October 11, 2015.

Spice writes: "It is often remarked about our engagement with Martin’s paintings that we are uncertain, when standing in front of them, where they reside. There are said to be three basic viewing positions: up close, from a distance and halfway between. At a distance – so this account goes – the paintings hide from us, close like flowers at the end of the day, retreat into impassivity, their details no longer to be seen. Up close, the materiality of paint, graphite and canvas asserts itself: lines that looked straight turn out to be subtly irregular, the spacings of an intricate grid are discovered to be subject to slight deviations, uniform colour fields to reveal delicate fluctuations in density – thinning here, pooling there. In the intermediate position, meanwhile, everything starts to swim, shimmer and pulse. In fact, things are a little less neat than this. Some of the paintings actually become more emphatic and distinct as one moves away from them; others so dazzle at close range that focusing on the detail tires the eyes; a few remain visually stable wherever one happens to be standing. But generally, in their shifting, mercurial nature, their having no steady state, the paintings can seem to elude us. What they exactly are, we cannot grasp. A consequence of their indeterminacy is that the paintings ask that we look, look and keep looking. They beckon us into an attitude of attention, a willingness to take time."