Anthony Caro, a friend of all the artists in the Cambridge show and a sort of honorary American, was inspired by the abstract expressionist sculptor David Smith: yet his intention was to become a greater artist than Smith had been.The disappointment of the Fitzwilliam exhibition is that such comparisons do not seem relevant. Poons, after his rather pleasant early period as an Op artist, wished to exceed Clyfford Still. If you don’t believe me, take your own colours into the Fitzwilliam and see if you can reproduce its results – and its conviction.Noland may not be so sublime an artist as his friend Morris Louis, but his colour has both a wider and a more subtle range It’s more potent than Louis’s palette. Just as one enters the exhibition, his Untitled of 1959-60 immediately announces a superb colourist. It’s made of 9 or 10 – my eye forgets – concentric circles: red in the middle, which is therefore the smallest area of colour, surrounded by white, then black, then white again, a yellow, a pink, a blue and so on Such a description sounds straightforward But its a complex, demanding picture. They sought a further purity, aerial and disembodied, with no reference to figuration, or to the metaphors for nature which underlay so much previous American Abstract art.Kenneth Noland banished metaphor by using the most basic forms, the circle, and by concentrating all his pictorial energy on the most abstract of all the components of painting, which is colour. For them, Abstract Expressionism had not been abstract enough.

This may be a nature painting, as Frankenthaler’s early works often were, but its goal was abstraction. Here was a mood and an ambition shared by the four painters now in Cambridge. And then there’s the haughty confidence of its improvisation Frankenthaler used thinned-down oil paint. She must have painted the unstretched canvas on the floor, quite rapidly, and was so certain that she had achieved her picture that much of this canvas was simply left blank.Indeed, the “swans” of the title are unpainted areas that happen to have a coincidental resemblance to birds Their depiction could not have been calculated.

For all its delicacy of feeling, somewhat concealed by a protective perspex box around the canvas, Swan Lake I is more obviously a grand museum picture than anything else in the Adeane galleries Its size is magisterial. Swan Lake I of 1961 is a moving link between Jackson Pollock (whose studio she had visited as a precocious young artist) and the open, expansive, coloured abstraction of the later 1960s. The phrase really meant that they belonged to the next generation of non- figurative artists after the collapse, or exhaustion, of Abstract Expressionism. Roughly, the most significant pictures from the Fitzwilliam painters came at the same time as Pop – a development to which they were opposed in almost every way.Frankenthaler (born 1928) is not the oldest painter in the show, but she has a close feeling for classic Abstract Expressionism. Bravely, but not deftly: rather dark rooms are not natural homes for modern art.