Visual art review: Fred Sandback - Minimalism? There's really nothing to it ...

The moment when artists abandoned their brushes, paints and bronzes and found art in new places is revisited at two exciting new galleries

Here's a treat for anybody as eager as I am to be transported back to the heady days of New York in the 1960s and '70s. That was when the old idea of art as a painted canvas or a bronze sculpture finally imploded, and the new idea blossomed that art might be the action of stretching a piece of string across a room or driving past the Guggenheim at 100mph.

The American Minimalist Fred Sandback was only 24 in 1967 when he created his breakthrough work, an outline in string and wire of a 20ft wooden plank that he had removed from the room. All that was left was the record of the object, yet the perception of the viewer was that the plank remained. For the next 36 years, Sandback experimented with creating illusions from empty space, his materials changing only fractionally as he progressed from string to his trademark lengths of coloured acrylic yarn.

Sandback was 59 when he committed suicide in his studio in 2003 and his estate is now represented by David Zwirner, the New York dealer who has recently opened a new London gallery in a converted Mayfair townhouse. This month, 12 pieces by the artist have been installed on two floors, the taut coloured yarns stretching from wall to wall or floor to ceiling as if Spider-Man had just spun them.

Sandback's work has been little seen in Britain, and this show is an informative introduction. In Yellow Diagonal (1974) the exquisite simplicity of the artist's practice is illustrated by a single piece of yarn which casts a shadow on the wall to complete a triangle. Meanwhile, in Two Part Standing Construction (1978), a pair of outlined squares set at right angles appear from some viewpoints as panes of glass.

Whether the effect here is quite as unsettling as Sandback intended seems unlikely: Minimalism makes very high demands on the spaces where it is shown and even in this simple white gallery, normally inoffensive details such as lighting tracks and air vents make harsh intrusions on the purity of the work.

Upstairs, however, there is a pure, unadulterated Sandback moment: here a set of orange outlines, from his Close series, form three oblongs stretched across a corner of the gallery. Free of unwelcome interference, these shapes appear to move before your eyes – a conjuring act of artful genius performed with only a few coloured lines.

Not far from David Zwirner is another new gallery, this one owned by Michael Werner, the German dealer who befriended many of the artists of the post-war period who followed the shamanistic teachings of Joseph Beuys. Among these artists was the Detroit-born James Lee Byars (Michael Werner Gallery, London), an eccentric figure who persuaded the renowned MoMA curator Dorothy Miller to let him stage his first show on a fire escape at the museum in 1958.

Around this time, Byers moved to Japan for nine years and his subsequent works and performance pieces – one of which was the 100mph drive past the Guggenheim – were often inspired by its culture, in particular the dramatised unfolding of lengthy pieces of hand-made paper. After Byars' death in 1997, in the suitably exotic setting of the Anglo-American hospital, Cairo, obituaries noted his penchant for dressing in gold suits, accompanied by a top hat and veil or, occasionally, a blindfold.

The show at Michael Werner – surely a precursor to a retrospective – displays early sculptures and remnants from his performances on a plinth, like relics in a museum. The meticulously preserved folded paper sheets from his performances – one of them over 100ft long – are shown in glass boxes like sacred objects. Alongside these are his roughly carved stone sculptures, together with an elongated wooden Self Portrait (1959), delicately laid out like a skeleton in an excavated tomb, all of which represent man in his most primitive form.

A second and larger room has been devoted to the display of a later piece called The Angel (1989). Over one year in Venice, Byars devised this sculpture made of 125 glass globes, each blown in a single breath by a Murano craftsman. The globes are laid out on the floor in a looping shape which refers to the Japanese kanji character for "man". So as we look into the room – it is arranged according to Byars's instructions as if the entire space were a vitrine – we see the essence of human life brilliantly distilled into these fragile and transparent little reliquaries.

Fred Sandback (020-3538 3165) to 16 Feb; James Lee Byars (020-7495 6855) to 16 Mar

Critic's choice

Two sumptuous photography exhibitions at London's Somerset House both end next week ... catch them before they close. Tim Walker: Story Teller showcases the fashion snapper's bright, playful, fantastical pictures and giant props, while Cartier-Bresson: A Question of Colour features 10 of the photographic master's prints never before seen in the UK, alongside 75 colour shots by other photographers inspired by his work, (both till Sun).