Fra Angelico to Leonardo

After taking us to China, Iran, Iraq, India, Mexico and Nigeria, the BM's latest exhibition looks no further afield than cinquecento Italy - but this too is a journey of discovery. It's also as scholarly and as comprehensive a show as you will ever see on fifteenth-century Italian Renaissance drawing, revelling in the medium's radical function as much as its finessed forms.

For the first time, artists could sketch ideas, compositions and figure groupings for paintings. They could easily map out a giant commission to show patrons, try out a tricky hand gesture or solve troublesome drapery details, all before committing brush to canvas. Much of the drawing boom was down to the advent of more readily available and cheaper paper - hitherto laboriously scraped and stretched goatskins were used - which one newspaper quipped last week was the Renaissance equivalent of the dawn of the iPhone. What nonsense. Paper was, clearly, the Photoshop of its day, a malleable, immediate and boundless field of experimentation.

Artists were also discovering their own voices. Even monks Fra Angelico and Fra Filippo Lippi began eschewing pure illustrative duties for virtuoso studies of human emotion, while Andrea Mantegna also turned to less pious subject matter for his 'Allegory of the Fall of Ignorant Humanity' that features a satyr and a donkey-eared fool leading a blind woman to the brink of hell. Another flight of fancy is Antonio Pollaiuolo's thoroughly modern reimagining of a lazy Adam rolling his eyes at Eve's inability to tame their little 'uns, Cain and Abel. The real temptations here are of the possibilities for racy depictions of the flesh or new fangled perspective scenes that would have been unpalatable or risky in paint. In fact, both of this show's juxtapositions of sketch to finished picture reveal the latter as comparatively precise, frozen and staid.

Despite the layers of scholarship needed to penetrate the subtler innovations in Renaissance draughtsmanship - the cartoon, the model book, the presentation drawing - there are reminders of what we should already know around every corner: Michelangelo's brilliantly overflowing pages reveal more than just the mind of someone who didn't like to waste paper and Leonardo da Vinci was also at his most quick-witted in front of a blank sheet of A3, or rezzuta as it was called in the 1400s. The show ends with the latent genius of these High Renaissance masters coming to fruition at the turn of the century with Raphael and Titian, yet it's the achievements of their precursors and teachers that really shine. Verrocchio's 'Head of a Woman', tilted to soften her delicately shaded features, must have taught Leonardo a thing or two and the flowing skirt in a Ghirlandaio might well have informed Michelangelo's dancing pen strokes.

The narrative hidden beneath those lines of influence is of the lost acres of works on paper that have been consigned to the rubbish or ravaged by time. If there's something strangely insubstantial and liminal about the examples here, it's that they only tell a fleeting part of that story. The BM and the Uffizi in Florence, the two pre-eminent collections in the field of Renaissance graphic art that put this display together, should be commended for bringing what remains out of their drawers and planchests, because the immediacy and flair of these drawings belie their age.