Frank Auerbach's paintings run gamut from horror to joy as Tate Britain shows

When Frank Auerbach was a few weeks away from his eighth birthday, his parents put him on a train from Germany to Britain. It was April 1939 and he would never see them again. Within little more than a decade, this orphan of the Holocaust would be exhibiting bold, pungent, paint-laden pictures that fascinated critics and fellow artists. In the 1950s art critic David Sylvester already thought young Auerbach might be a "great painter".

Another fan was Lucian Freud, nine years older and already established, who came to an Auerbach exhibition and simply said to the artist: "Thank you." They were to be close friends until Freud's death in 2011.

Freud has left his friend an extraordinary gift. The bequest is technically to the nation. Freud's collection of 15 paintings and 29 drawings by Auerbach has come to the British government in lieu of inheritance tax. It is now on view at Tate Britain, in central London.

Freud's choice of his friend's art is superb. The troubling, profound masterpieces he owned open up new ways of seeing Auerbach and will surely win him new generations of fans as he prepares for a Tate retrospective in 2015.

In one painting, a woman stares into a fire - says the title. Yet it's hard to see a face in the chaos of ripples and strings of paint. Freud owned a drawing done "to elucidate" this painting - it seems the great realist painter wanted a key to his friend's near-abstract image. Such shocking and strange accumulations of paint are what make Auerbach so radical and disconcerting. The ripe, raw textures of his thick, heavy creations make them almost impossible to photograph as he takes painterliness to a visceral extreme, laying on great rivers, mounds, twisted braids, spiky hardened drips and straight-from-the-tube loops of colour.

Auerbach is very different from Freud and has more in common with Swiss existentialist Alberto Giacometti or American abstract expressionist Willem de Kooning.