Raoul de Keyser's show at the Whitechapel Art Gallery is one of the most tantalising and elusive I have ever encountered. Hovering on the border between representation and abstraction, it hints at his lingering involvement with the visible world. We catch glimpses of an attic, a monkey- puzzle tree, a valley and other, less identifiable subjects. But de Keyser doesn't let us forget that we are looking, fundamentally, at coloured marks on canvas.
Based in the small Belgian town of Deinze, this retiring artist has never strayed far from home for inspiration, and only recently gained an international reputation. For more than 40 years, he has pursued his own quiet yet rigorous path. But it would be a mistake to conclude that de Keyser is a limited painter, confined to a narrow line of inquiry. The work assembled in this major retrospective, spanning the period from 1964 to last year, has a very open-ended feel.
The earliest paintings are the most quirky. Fascinated by the war waged in the early 1960s between hardline American abstractionists and renegade artists, he gave up his job as an arts and sports journalist to do pictorial battle in the studio. Mischief-making is evident straight away with a painting called Baron in an Al Held Field. Although most of the canvas is handled as a smooth expanse of brilliant yellow, reflecting his interest in Al Held's abstract work, a roughly textured image of Baron the dog barges in. He looks like an unruly, smiling figure from an expressionist painting, and his presence here makes us wonder if the "field" could instead be a football pitch.
De Keyser's love of sport emerges frequently in his early pieces. A large, free-standing, box-like work from 1971 looks at first like a severe minimalist painting aspiring to the condition of sculpture. But then we realise that the white band travelling round the sides of this otherwise deep green structure could be the edge of a sports ground, or alternatively a goal. De Keyser has left the question as wide open as the putative goalmouth.
He often works in clusters, and three paintings from 1981 are called Tornado. Yet they could hardly be more different. One is divided, very starkly, between more or less equal blocks of white and black. It reminded me of the very subdued paintings produced by Rothko just before he committed suicide. The other two are far more turbulent and free. One, an unusually tall work, is scythed from top to bottom by a jagged line of brightness. The third is still more disjointed, contrasting a supposed lightning bolt with a fractured, pierced oblong reminiscent of something broken and hurled through space by a storm's headlong force.
In his subsequent work, de Keyser has moved restlessly from one extreme to another. The three canvases from the Gate of Hell sequence become increasingly unstable, culminating in an image where everything seems to break up into suspended particles. But this uneasy series is succeeded by a group of interiors where forms suggesting windows, blinds and doors glow with luminous power. They show de Keyser as a master of stillness, celebrating the quiet serenity of domestic spaces. Even so, he reacts against their peacefulness soon enough. In a small picture tersely entitled Z, he scrawls the capital letter across the surface of a canvas as besmirched by hasty, impulsive scribbles as a graffiti-smothered street wall.
By the time we arrive at Dalton in 1990, stasis has returned. A khaki ground lends the painting a flattened-out sobriety. The four dots of darker, bruise-coloured pigment do little to disrupt the general equilibrium, and yet they gradually take on the appearance of holes piercing the canvas. In a rare moment of revelation, de Keyser has explained that the picture's title refers to the Dalton Gang, a belligerent group of Kansas gunslingers who lost four of their members in a showdown in 1892. So the "dots" could be bullets travelling towards the doomed men, or cavities left in the canvas after the shoot-out had finished. Either way, they are redolent of death and usher in a whole series of paintings where misty surfaces become invaded by smaller, more numerous "dots".
As the 1990s proceeded, and de Keyser approached his 70th year, his work grew more concerned with vulnerability. Torso, a particularly fragile painting, appears to expose the rawness of burnt flesh, while the minuscule flicks and flecks of paint darting over its dusty pink surface look like injuries sustained by the skin. We still come across the old football pitch motif: Ground, a canvas begun in 1971 but not completed until 1995, reasserts the crisp, heraldic geometry of white markings on deep, rich green. But the forms in other works from the same period become notably blurred, as if threatening to dissolve into the hazy pigment around them.
In Return 2, painted by de Keyser at the end of the 1990s, everything has splintered. Perhaps inspired by bare winter branches and birds with strangely etiolated wings in mournful flight, the work has a skeletal structure. All the same, there is no suggestion that de Keyser is ready to retire: neither of his paintings from last year, Prologue and Precedent, indicates any decline of pictorial energy.
"Raoul de Keyser" is at the Whitechapel Art Gallery, London E1 (020 7522 7888) until 23 May