He comes in colours: Craigie Aitchison at the Waddington Custot Galleries

Scottish painter Craigie Aitchison was dismissed by some critics as twee. But the brightness and warmth in his work give it a compelling edge, as Adrian Hamilton discovers at the first show since the artist's death

While most of his contemporaries were slapping on the paint, Craigie Aitchison went thin, so thin his diluted oil paintings of skies and flowers and dogs became almost translucent. Yet they always retained a colour and a life which remained unique to himself.

Aitchison, who died in 2009, was always a one-off in subject matter as in style. His precise, usually small, visions of the crucifixion set on barren land, his Bedlington dogs and yellow canaries, the still lifes with a single flower, the images of birds and trees and the portraits, flat and angular, make him instantly recognizable and curiously compelling. In a lesser artist his style might be considered one for the postcards (which they often were), in a more dramatic artist it might be thought of as wet. But in his brushwork he was supremely committed, and supremely good.

The new exhibition at the Waddington Custot Gallery in London is thus doubly welcome. It is in the nature of a retrospective of 49 works covering most of the themes and the mature decades of his work, from the late Seventies until his death. As such, it misses the paintings from the late Fifties and Sixties when the young Scot was still finding his way in London and became obsessed with painting black models on the grounds that he liked the effect of colour on dark skin. But it covers most of his years of maturity when his style seemed to find its natural pace and subject matter. It is also in the form of a private collection, now up for sale, built up by one of that now disappearing breed – patrons who collected in depth rather than trophy hunting for the best in all.

Sheelagh Cluney was an Irish critic and writer who came to England after 18 years in Japan with the clear ambition to collect paintings from one living artist. She met Aitchison, drunk but not disorderly, at a show in Kettle's Yard, Cambridge, in 1979 and immediately bought a picture – the fine portrait of Mark Fry with striped shirt and a bird on his shoulder of 1979. From then on she was a regular purchaser of his new work until a few years before his death. They were not kindred spirits exactly. She was an Irish woman given to speaking her mind, he was a deeply private man quick to anger and slow to forgive. But, in this case, the friendship was a fruitful one. She had a keen eye, refined in Japan, for the spare and the still in his work. Aitchison's portrait of her from 1990, in black tailored top with a crow chirping beside, presents her as both inquiring in her light blue eyes and severe in her compressed mouth.

“Idiosyncratic” is the usual deprecatory term applied to individualistic artists such as Aitchison. It shouldn't be for it implies a naive primitivism of the self-taught. Aitchison was anything but. The son of a Scottish judge, he studied law at Edinburgh University and the Middle Temple before taking up painting and going to the Slade, where, along with Michael Andrews, Paula Rego and his lifelong friend, Euan Uglow.

He compared it to his legal studies. “With a picture you've got to get it precise or it's wrong”, he is quoted as saying in Andrew Lambirth's introduction to the catalogue. “Law is also about getting it right or it is lost.” That is not entirely true of the law. Performance matters in courts. But it was certainly true of Aitchison's approach to painting. Where Euan Uglow sought exactitude in geometric precision, Craigie sought it by a constant reworking of the surfaces. Leslie Waddington thinks he must have been influenced by Mark Rothko in his use of broad horizontal plains of colour as by Milton Avery in use of thinned oils.

Aitchison retorted that he didn't even like Rothko, which was probably correct in that his whole artistic credo was at odds with Abstract Expressionism. But in style there were clear similarities, most particularly in the two fine bigger pictures in this exhibition, Holy Island, Isle of Arran from 1993 and Crucifixion from 1984, with their emphatic division of space into horizontal blocks of colour. Although always a figurative artist, Aitchison's approach to actual paining verged on abstraction.

His images were rooted in his own experience – the woolly Bedlington dogs he loved so much, Goat Fell mountain on the Isle of Arran and Holy Island in the Firth of Clyde that he remembered from his childhood, the dead bird he found frozen on his windowsill. But he introduced them into his pictures quite spontaneously. To critics there was something repetitive about this, even twee. But the individuality and warmth of his work comes from the way he develops each theme afresh. Two pictures of washing lines at his house in Montecastelli in Italy see the lines placed centre in the lower half of the picture, but in one two square items hang rigid be tween two poles against a green background while in the other items of clothing hang between two bare trees against blocks of blue and brown with a black night sky barely lit by the moon. The effect is quite different, one solid and fresh, the other wistful. The formalism of his composition saves his pictures, as in the deeply felt tribute on the death of his pet dog, Sugarbush Dead from 1982, with its dramatic diagonal shaft of light illuminating the head of the animal.

Quite why he took to the theme of crucifixion is a question he declined to answer other than saying that it was a “good story.” Coming from a Scottish family in which a grandfather was a minister in the United Free Church, there's something more to it than that. The pictures found a ready ecclesiastical market but in their pared-down, isolated imagery are far from representations of the Passion. Instead, they have majesty in the deep colours behind the hanging figure and the bare trees and a frailty in the small sometimes limbless figure hanging lifeless from the cross.

Few would argue that Craigie Aitchison belongs to the first rank of postwar British artists. He lacked, I think, the self-confidence, or the reach, for that. But he was a wonderful painter and the Waddington show is a perfect way to succumb to his charm.

Craigie Aitchison: a Private Collection, Waddington Custot Galleries, London W1 (020 7851 2200) to 6 April