""No art that is not intellectual can be worthy of Scotland," said David Wilkie, speaking at a dinner in his honour in Rome. So was one of our greatest painters an early champion of conceptual art? Far from it. He could not have imagined an art in which the coordination of hand and eye was not the first principle. What he meant was that art needed mind as well. People have thought hand and eye were enough. Others now argue that intellect, or what passes for it, is all it takes, but great art needs all three: hand, eye and mind.

That is why Wilkie would have recognised Ken Currie as an artist worthy of Scotland. He is a master of  the  business  of painting, of hand and eye, but he does not stop at that. He uses his command of his means profoundly to comment on the world and cast some illumination in its dark places.

His exhibition at the Scottish National Portrait Gallery is simply called New Work, but it is new work done for this place: a soliloquy on the business of portraiture and the idea of a likeness.

Planning the show, however, he found, in keeping with the modern notion that art is all ideas, the new contemporary art space in the Portrait Gallery actually has no walls to hang paintings. So they had to build a room in the middle of it. Painted grey, it's like a mausoleum, Currie says, and the sombre mood of his paintings suits it.

Currie is of course no stranger to the Portrait Gallery. Some time ago he painted for the collection the triple portrait of oncologists, Prof R J Steele, Sir Alfred Cuschieri and Sir David Lane. It's a haunting picture of three eminent surgeons working at the cutting edge of medicine, and for once that hackneyed phrase is pertinent as they wield their scalpels, dealing with life and death and the mysterious, frightening illness that creeps up inside us without warning. The portrait captures all of that. It puts the oncologists, serious and intent, in the frontline of a struggle with death.

Preparing for the portrait, however, Currie declined to use photographs because, being pictures already, they would pre-empt his image. Long sittings were out of the question, so he made life-masks. Death masks are more familiar, those macabre souvenirs of the death bed, doubly dead, their faces sunk in death rendered in dead white plaster, but life masks are equally strange. They have all sorts of resonances: is the face a mask? Can a portrait be any more than that?

This theme is set by Mask, a small tour de force at the entrance, a painting, not of an actual mask, but of the mould, the negative image of a face. Much of the inside-out face is in deep shadow, but strong light falling on the rest of the mould casts reflected light into this shadow with the startling effect that it flips back again; the negative becomes positive and we can read the face as though in relief. We are left wondering where the likeness lies: in the mould, in the artist's mind, in our eye, or nowhere?

Masks recur in several paintings. Night Work, for instance, is as dark as its title. A figure lies as though on a bier, white and featureless as though in a shroud, head towards us and feet pointing into a dark opening framed by crimson curtains. It looks like a body in a crematorium ready to slip through the curtains into the  furnace, but a bucket beneath its head catches drips of white plaster as a mask is applied. Two solemn figures stand at either side. They might be surgeons, but one is wearing an apron and gloves caked with plaster, the other is holding a spatula.

When a cast is being taken, you have to lie still as death. It's a weird mixture of the rituals of death, of medicine and of art, all in pursuit of a likeness.

Plaster Setting is similar. A man is laid out on a table, his face coated in plaster. Otherwise he is naked except for a pair of crimson velvet slippers. There's a bucket behind his head and an enamel jug at his feet. This is all quite matter of fact, but candles on the wall create a quasi-religious gloom. Beyond the figure is a framed recess. Within are more dark red curtains, but also an old fashioned bath with no taps. Or are we looking into a mirror? If so, where are we?

The bath and also a cloth on the table pay homage to JL David's Death of Marat, a martyr portrait of one of the heroes of the French Revolution, murdered in his bath. Because of its revolutionary potency, David's painting of the dead Marat became paradoxically a live image.

Currie's picture is also a fitting tribute to the classical language of painting, light and shade, depth and surface, from one who is himself a master.

On the opposite wall, Effigy echoes the composition of Plaster Setting. The effigy of an ecclesiastic is laid out in silk and velvet. His face is a mask and he's wearing crimson velvet slippers.

The mirror in Plaster Setting, if it is a mirror, is a reference to Velazquez's Las Meninas, an extraordinary soliloquy on the elusiveness of the painted world. Currie also tackled the challenge of Velazquez in his self-portrait. He is standing naked, stooped and prematurely aged in front of his own reflection in a tall mirror.

He returns to the theme of mirror images again here, too, in Mirror, a head seen from behind blocking out its own reflection, and in Imago where the sitter stands in front of his own portrait, identical except that, like Dorian Gray, the portrait shows his younger, less corrupted self.

In Narcissus, too, Currie works an ironic variation on Narcissus's story of reflective self-regard. A man is standing waist deep in water looking down at his reflection, but he is not young and beautiful like the mythical shepherd. He is middle-aged and bald with a comb-over, ultimate absurdity of the narcissistic.

There are hints of the artist's own appearance in some of these paintings, but they are not self-portraits. His own face is just the handiest reference, he says. This is most apparent in one of the strangest pictures here, the Double. Two portraits side by side are apparently identical. At one level it was just an  exercise. He set himself the challenge of painting two identical portraits. But there are other levels too. The face is an amalgam of the artist's own and General Franco's. Not out of any admiration for Franco, however. As dictator of Spain Franco's face became an icon of ruthless power. Here that subliminal reference adds an unsettling, half-recognised familiarity to the face. Thus this hypnotic painting invokes the strange myth of the sinister double, the doppelgänger.

It is a significant motif in Scottish literature, appearing in James Hogg's Confessions of a Justified Sinner, most famously in Stevenson's classic of the genre, Jekyll and Hyde, but also, says Currie, in Markheim, another strange Stevenson story. A man commits a murder. He is justified in his own eyes like Hogg's Justified Sinner, but with blood still on his hands, he is confronted by an apparently genial, but uncanny figure who "at times he thought bore a likeness to himself".

Ken Currie belongs in a great and distinctively Scottish imaginative tradition. We have to thank the Portrait Gallery for bringing us such first-class contemporary painting."

Ken Currie is at the Scottish National Portrait Gallery, Edinburgh, until 22 September.

Duncan Macmillan

 www.scotsman.com/lifestyle/arts/visual-arts/ken-currie

 www.nationalgalleries.org