Art review: Calum Colvin, Natural Magic

***** ROYAL SCOTTISH ACADEMY, EDINBURGH

ART and science don't mix. It's axiomatic, but is it true? The two branches of human inquiry were originally two aspects of the same endeavour: to understand the world, not by precepts given by God, but by describing it and finding out how it works. Dutch scientists were at the forefront of empirical science, and alongside them Dutch painters explored how the world looks. Vermeer, for instance, lived and worked in Delft, a centre in the development of optics, and his art is preeminently about seeing.

But Vermeer's wonderful paintings also demonstrate that where science must seek certainty and claim detachment, art can harbour doubt; that seeing is not simple and objectivity is an illusion. As it was formulated by Hume, this insight shaped our understanding of the world, and modern art with it. The camera, with all the ambiguity that surrounds its promise of truth, also encapsulates the idea. If they had been separated, art and science were also rejoined in photography. Calum Colvin is a photographer who explores the implications of those awkward facts about perception, the complex questions that spring from them and how these reflect on our relation to the world around us, even on how we construct our sense of ourselves. The latter inquiry he shares not only with Vermeer, but with Rembrandt before him. In his self-portraits Rembrandt was the first to follow the apparent truth of empirical observation to the point where it breaks down into uncertainty and doubt in the inescapable subjectivity of self.

Colvin makes photographs, but by a complicated route. He constructs the image in a three-dimensional assemblage, sometimes also partly painted. He turns that compound image into a flat photograph, but then, to complicate the issue further, the photograph is printed onto canvas and presented as a painting. In Natural Magic at the Royal Scottish Academy these flat pictures, his photo-paintings, are then bounced back into three dimensions – or at least that is how we see them.

Colvin's title is taken from Letters on Natural Magic addressed to Sir Walter Scott by Sir David Brewster. In the book, Brewster's subject was illusionism generally, but he has no doubt that "the eye is the most fertile source of mental illusions". Brewster was a combative Scottish polymath. His scientific publications were copious and diverse, but his central interest was optics. He invented, and named, the kaleidoscope, but he is principally remembered for the role he played in establishing photography in Scotland. He managed to persuade its inventor, Henry Fox Talbot, not to seek a patent here.

Thus Hill and Adamson, encouraged by Brewster, were free to pioneer it as an art form. Like all Scottish photographers, Colvin therefore stands in Brewster's debt and this show is in part a generous acknowledgment of that.

Another of Brewster's inventions was the lenticular spectroscope. It also became a favourite Victorian scientific toy. You look at two photographs taken from a slightly different angle through lenses in a viewer arranged so that one eye sees one image and the other eye the other. The result is stereoscopic vision. The two flat pictures are transformed into a single three-dimensional image, or at least that is what we see – natural magic indeed. Brewster's invention deployed photography to develop an earlier invention by Charles Wheatstone, however, a stereoscope that used paired drawings seen separately by each eye in paired mirrors mounted at an angle.

Brewster and Wheatstone became bitter rivals. As we enter Colvin's exhibition, there they are glowering at each other across the room and in three-dimensions, too. Colvin has adapted Wheatstone's mirror stereoscope. The portraits are doubled, each photographed from a slightly different angle. Between each pair an angled double mirror is mounted so that, standing close, we see the reflections of the pictures on left and right separately with our left and right eyes. It takes a moment to adjust, but then the pictures converge and jump into a single three-dimensional image; but what are we seeing? What started as a three-dimensional assemblage was turned into two flat pictures and now it exists as a single image again in three dimensions, but only in our heads. Where indeed does the truth lie in photography, or in painting, or indeed in sculpture, the three-dimensional art? (The mirrors are mounted on sculptor's modelling stands.)

Within the image too, nothing is simple. Both Brewster and Wheatstone's faces appear to be projected over the furniture in the artist's studio and so are intersected by things, such as a ladder, also seen from a different angle reflected in a mirror within the pictures. It is symbolic too, representing ambition. In a corner the English flag and the Saltire jockey for position in our eyes and poor Wheatstone is haunted by little images of Brewster.

In the row between them, Brewster thought he had trumped Wheatstone's claim to have invented stereoscopy with the discovery of two apparently stereoscopic drawings by Italian Renaissance artist, Jacopo Chimenti. Colvin revisits this controversy by reworking Chimenti's drawings. To Brewster's chagrin it was demonstrated that they were not actually stereoscopic. Wheatstone's claim was safe and they hang side by side on the wall, flat pictures. But apparently you can also look at them through a Brewster stereoscope and so they appear to be in three dimensions, after all. What you are actually seeing, however, is a stereoscopic image inside the viewer. Brewster wins. Colvin records the drawing as a projection and Brewster's ghostly face glares out through it. In the mirror stereoscope what we see is manifestly a mental construct. It is not in front of us. It is in our heads. Art and science mix inextricably in the elusive psychology of perception.

In portraits of Burns and Byron, Scottish Bard and Anglo-Scottish romantic, Colvin has used this effect to explore the elusiveness of identity, just as he did so successfully in his recent Ossian series. But then he moves into a different mode. For the other works in the show you have to don the green and red spectacles of anaglyph 3-D. The image is repeated in red and in green. These are laid over each other, but offset. The lenses cancel one colour for each eye and so the offset between the two images creates a single stereoscopic one. It plays games with a different part of our visual perception, but the effect is even more mysterious. Things can appear and vanish again.

Colvin has used this effect in a picture of hands in a shadow play making a rabbit on the wall. It is an elementary illusion, but photography too is really just such a shadow play. Alongside is an image of a skull and candle. It is a traditional memento mori, but its message has a new twist. A ghostly presence, the candle comes and goes as you watch it. He has also set this 17th-century image in the tiled interior of a Dutch 17th-century optical peep-show made by Samuel van Hoogstraten, a pupil of Rembrandt, and so by a natural progression of ideas, Colvin makes his own self-portrait, also to be seen through the red and green spectacles. Apparently hovering above the same tiled floor, he is peering at us through a glass slide, a stage in the making of his picture. In the other hand he holds an ambiguous perspective diagram that doubles as a Saltire. His hand holding the slide is a complicated piece of illusion involving an internal reflection across the picture space.

But what is he seeing in the slide? Us or himself, or both, and where is the image? As Rembrandt realised, the self-portrait encapsulates all the ambiguities: who is seeing what; what is the object and what the subject? Is it possible to project the basic fact of self awareness? And then in addition, where in all this is the photograph? What kind of truth does it convey? As Colvin's self-portrait jumps into a shifting, three-dimensional image, all those perennial questions are raised anew.

&#149 Until 5 April