Anonymous: Portrait of a Young Man (C80-120)

What's more realistic? Imagine a detailed line-drawing of a face, describing its every nook and cranny, every lash and hairline wrinkle, the pores of the nose, the furrows of the lips, the eyeballs' veins, the radiating fibres of the iris. And imagine next to it another image of a face, entirely omitting these minutiae, a broad-brush sketch in ink, which renders very clearly with light and shade the solid volumes of the head. Which is more realistic?

No answer, really. It depends. The reality of a head has a number of aspects to it. It depends what you're interested in. The two images carry different kinds of information. If you want to know the precise shape of the eyebrows, then it's the detailed drawing that will seem more realistic. But if you want to know the general set of it, the bumps and hollows, what protrudes and what recedes, then the 3D modelling of the sketch will have the more telling realism.

Try another, slightly different question. Which is more lifelike? Imagine a sculpture made from a life-cast of someone's head. Quick-drying plaster has been applied. A succession of readings has been taken from all round the head, and assembled into a single mould. A piece of bronze is cast. The result is an exact copy of an individual human head.

Imagine another sculpture, roughly fashioned from wood or stone, providing only the most schematic likeness of a human head. There's a sticky-out nose. There are two eyes and a mouth - but these aren't carved, they're just painted on to the surface, big dark pupils in bright white eyeballs, and a big red mouth, and the whole object is painted in something approximating to a flesh colour. Which is more lifelike?

Again, it depends on the kind of lifelikeness you're after. Which head more closely resembles a normal specimen of humanity? The first, obviously. But which head is more likely to give you the impression that there's someone else in the room? The second. If it's a sense of living human presence you want, the perfectly accurate monochrome clone won't do it. It's the crudely modelled, boldly painted effigy, staring eyes and gaping mouth, that will push our buttons, send out the essential and irresistible signs of life. Of course, you can sometimes have it both ways.

The life-size portraits excavated in the Fayum region of Egypt are a fusion of traditions, an intersection of Egyptian and Graeco - Roman visual culture. The local artists who made them adopted the observational techniques of Greek painting. But the function and much of the force of these images belongs to Egyptian religion and burial practices. These face-pictures were fixed to the heads of mummified corpses. They gazed out, framed by the mummy's bindings. Their job, as with Egyptian funerary art generally, was to preserve the life of the immortal spirit on its journey into the next world.

These images had cross-purposes. They used a style of painting designed to capture the likeness of a living individual. All the evidence suggests that they were indeed painted from "the life" - perhaps immediately after death. But they weren't made, as Classical portraits were, to impress human viewers. They were made to be buried, to carry the soul of the departed on its way - and the pursuit of afterlife was an Egyptian, not a Classical, thing. So these mummy portraits embody two distinct kinds of lifelikeness.

The pictured dead are often young. (Life-expectancy was low). This portrait of a young man with a bare torso may depict an athlete or an initiate of the Isis cult. And in terms of taking an individual likeness, it's a highly accomplished work, a sensitive instrument for registering the particulars of a face.

The artist has an efficient "identikit" system at his disposal - the same basic system that is still used today by pavement artists throughout the world. The face is approached as a series of multiple-choice options. Overall shape?

Disposition of features within this shape (proportionate lengths of brow, nose, upper lip, chin) ? Shapes of single features (bridge of nose, nostrils, lips etc)? The portrait puts a list of questions to the face, questions that each have a limited number of possible answers, and applies the answer that fits best.

What's impressive in this picture is that the questions are not only about the "name" features. They also concern the moulding of surrounding areas, like the eye sockets, the cheeks, the flesh round the mouth. And its answers are confident but unexaggerated. Look at the slight indent of the cheek: the shaping stroke is definite, not fudged, but the range of light and shade used is strictly limited. Equally, look at the subtle modelling of the lower lip, the light, barely visible touches of moustache. Or the masterfully steered curve of the upper lip. Everything is sure but restrained.

A likeness, then. But a likeness, however finely done, does not make for life. And it's life, the spirit, rather than mere individuality, that must be asserted in these portraits of the dead. So there is a point where all of them, even the most sensitive, abandon their observational enquiry. The eyes! The eyes, emphatic, enormous, darkly ringed, blaze out of the face, with the force of the eyes of a Pharaoh.

In some of the mummy portraits, the eyes are so big and round and strong they take on a life of their own, upstaging the rest of the painted face entirely. By comparison, the maker of the image here manages the effect with (characteristic) restraint and skill - those finely placed gleaming highlights! But the effect is still there: the sense that the portrait is inhabited within. The eyes don't so much belong to the face, as stare out of it, like human eyes staring out through the eye-holes of a mask. The look of the mortal individual is recorded. The immortal soul burns through.

THE ARTIST

The Fayum mummy portraits, painted in the first and second centuries, preserved in the dry sands of Egypt, and mainly dug up again in the late 19th century, are one of the most remarkable survivals from the art of the ancient world. They're a great mix-up. Their styles range from stark graphic simplicity to the most fluent impressionism. Their subjects reflect the ethnic diversity of this Roman colony, with a whole spectrum of skin colours. And in the work of these anonymous but often extremely gifted Egyptian artists we get the only serious glimpse of what Classical easel-painting - much praised by commentators, but otherwise entirely lost - might have looked like.