The art of the Renaissance: In the line of beauty

Are the drawings of the Renaissance masters more illuminating than the paintings themselves? Michael Glover is awestruck at the British Museum

At about the beginning of the 15th century a profound revolution took place in the way art was made in the Western world. In 1413, the great Florentine architect Filippo Brunelleschi discovered linear perspective, enabling artists not only to create a seductive illusion of a three-dimensional world on a flat, two-dimensional surface for the very first time, but also to combine real and imaginary space in a single painting. A new human-centred naturalism, based on drawing from life, entered into art. At the same time there was a quickened interest in the arts of the classical worlds, a new wish to profit by the lessons to be learned from the Greeks and the Romans. This was the very meaning of the Renaissance: a re-birth of learning and skills, a rescuing of that which was at risk of disappearing forever. And, just as important, drawing came to be practised as never before.

This great show at the British Museum, assembled in collaboration with the Uffizi's Gabinetto Disegni e Stampe in Florence, is a survey of what happened to drawing in Italy from the beginning of the 15th century to that moment about 100 years later when Michelangelo and Raphael decamped to Rome, and helped to initiate a quite different phase in the development of the art of the Renaissance.

This show does not merely show us about 100 of the greatest drawings in the history of Western art by the likes of Mantegna, Fra Angelico, Botticelli, Michelangelo, and Pollaiuolo. It is also a kind of master class in the practice of drawing. It shows us how drawings were executed; it explains why the art of drawing came to flourish to the extent that it did; it makes clear to us why drawing was so useful to artists.

Technology helped to make drawing popular. Drawing on vellum, an expensive process, began to be replaced by drawing on paper at the turn of the 15th century. An inventory of 1476 tells us that the cost of a sheet of vellum was precisely 14 times as much as a sheet of paper. Engraving began to make the wide dissemination of images possible. Artists would no longer be dependent on model books as a source of imagery. What is more, the replication of images meant that the possibility of far-reaching fame would be more readily within their grasp.

This exhibition, in addition to displaying drawings, gives us all the nitty-gritty of the making of drawings – a sample of sheepskin vellum to touch and to compare with a sample of hand-made rag paper; various quill pens. Samples of model books give us marvellous drawings of animals, often in profile. Animals featured regularly in model books because they were so useful to artists. They could enliven a scene, add touches of decorative humour and irreverence, stand proudly at the centre of an armorial device. What is more, the coats of animals never go out of fashion.

Many of the drawings in this show have seldom been on public display. Most were studio works, not made for the eye of the general beholder. They were private matters, or objects to be seen by a patron alone, evidence of work in progress. We may know the finished altarpiece, but we are unlikely even to be aware that these drawings, many of which were milestones along a long and increasingly potholed road, even existed. Why did they come about? They became increasingly necessary because the great patrons of Florence, Venice, Milan, Mantua made greater and greater demands of their artists. As their coffers and their heads swelled, their schemes of civic aggrandizement grew in ambition and complexity. In order to get to grips with such commissions, the artists needed to make multiple drawings – of figures, of drapery, of architectural details. Of these elements, singly. Or of all the elements together, to see how they fitted. They excite us because of this very fact – that they were provisional, subject to changes of mind, refinement. In this show, for example, there is a study of drapery by Ghirlandaio, made in 1491, just a tiny part of an immense whole, but a crucially important one all the same. He has arranged the material just so, having first dipped it in liquid in order that it shall retain the precise fall of its folds as he draws, and draped it across a jointed wooden figure. Precise effects are calculated in order to render the correct degree of light and shadow, weight, definition – see Andrea Mantegna's brilliant late drawing of a young Man Lying on a Stone Slab, which combines black chalk with pen and brown ink.

Elsewhere a single sheet of drawings by Leonardo contains a multiplicity of rapid ink sketches of the same subject – no one drew more rapidly than Leonardo when he was on heat. We see him testing, playing with, the poses. There is often a degree of almost unimaginable irreverence on display here. Look at a sheet of drawings, also by Leonardo, showing the Infant Jesus roughing and tumbling it with a cat, for example. Would that ever have found its way through the doors of a church? Not on your nelly. We see artists wrestling, almost in the abstract, with the marvellous challenges of the new. Paolo Uccello's drawing of a chalice (1450-1470) looks like an extraordinary technical challenge that he has set himself: to subject the shape of a chalice to pictorial, geometrical analysis, involving more than 2,000 intricate points of intersection. Just to look at it, and in so doing to re-experience the intellectual and emotional excitement that he must have felt as he explored the repercussions for art of the truly breathtaking discovery of linear perspective, still takes your breath away, even in 2010, as jet planes once again deposit their filth overhead.

Drawing can lay an artist bare, reduce him to the very essence of himself. Stare at a wonderful drawing by Botticelli here called Abundance or Autumn, which dates from the 1480s. It is every inch the essence of the Botticelliness which he brought to an extraordinary degree of artificial perfection in such paintings as Primavera, and which he later learnt to outgrow (somewhat) thanks to the stern, apocalyptic preachings of Savonarola. Here is the typical, exquisitely empty-headed Botticelli damsel, with her diaphanous, wind-ruffled draperies. And it is all here, in the drawing. Botticelli knew to perfection what a Botticelli woman was, even before he scaled her up and plied her with heavenly colour.

But the Italian word disegno means more than mere drawing. It also includes the idea of conceptual design, first the imagining and then the development of complicated ideas. Where exactly is this particular saint to be placed in this altarpiece, and how is his placing to relate to the position of the donor who is paying for it, and who is expecting it to be, in part at least, an exercise in self-aggrandisement? All these were ticklish matters with potentially immense repercussions, both aesthetic and political. These artists, as the show demonstrates again and again, had to be masterful players both in the world of the studio and outside too, in the brutal, vengeful world of cultural politics.

Fra Angelico to Leonardo: Italian Renaissance Drawings, British Museum, London WC1 ( Britishmuseum.org) to 25 July

For further reading: The Psychology of Perspective and Renaissance Art by Michael Kubovy