Putting on an exhibition of Monet is a guaranteed crowd-puller, yet increasingly difficult to justify nowadays.

When seemingly every aspect of the arch-Impressionist's long career has been examined in a long sequence of blockbusters, how do you find a fresh angle?

The Unknown Monet, just opened at the Royal Academy, has come up with what might seem a surprisingly obvious one. First staged at the Sterling and Francine Clark Art Institute in Williamstown, Massachusetts, it is the first substantial exhibition to be devoted to Monet's works on paper.

Though presented in the Royal Academy's smaller Sackler galleries and relatively modest in scale, it boasts a telephone-directory catalogue containing new research which sheds light on Monet's formative years in Le Havre.

About 500 works on paper - mostly drawings in pencil, charcoal and pastel - are known to have survived. Though many are in private collections, the description "unknown" seems a slight exaggeration, in that a fair number have found their way into museum collections, particularly in America.

But it is true to say that Monet's drawings have had little attention, and it also appears that, as one of the first artists to cultivate his own image through the medium of the newspaper interview, this is something he actively encouraged.

Apparently it suited him to promote the image of the "pure" Impressionist painter who began each work with a blank canvas in the open air, without the supposedly stultifying influence of preparatory drawings.

It is not particularly surprising to discover that this was only a partial truth. As Monet gravitated towards an artistic career in his teens he began by sketching landscapes, and his first paid work as an artist was as a caricaturist. Later he drew extensively in pastel, and even the late large water-lily paintings were preceded by compositional sketches.

But as this exhibition makes clear, graphic work never held the importance for Monet that it did for his Impressionist contemporary Degas. That is partly because Degas' main focus was the human figure, and when you are dealing with the figure there is no getting away from the discipline of drawing.

This is demonstrated by the first exhibit from Monet's maturity in this show, which comes after an opening selection of juvenilia consisting of some of the caricatures - a self-contained body of work which emulates an established mid-19th century style - and some unremarkable landscape sketches.

In 1865 Monet attempted a hugely ambitious figure composition, Le Dejeuner sur l'Herbe, in obvious emulation of Manet. There is no way an artist could have embarked on a project of this kind without making numerous preparatory drawings, and the exhibition includes two - a study of the female figure on the left and a rough sketch of the complete composition.

But this painting caused Monet great difficulties and he did not continue down this road, turning instead to landscapes on the familiar easel-friendly scale of classic Impressionism. Still, if figures - or cows - appeared it was still advisable to make some pencil studies before setting up the easel.

All of Monet's pencil drawings have this functional character: he never seems to have been interested in working them up for exhibition. To see them at their

most raw you can leaf through a group of sketchbooks (electronically, by touch-screen technology) preserved in the Musee Marmot-tan Monet.

He was delightfully haphazard in the use of these sketchbooks: the first was started in 1865 and picked up, after a gap of decades, in 1919, while another spans the years 1886 to 1925.

From as early as the mid-1860s Monet was drawing pastel landscapes, particularly on the Normandy coast. They include studies of skies and light effects which bring Constable's cloud studies to mind.

But while they reflect Monet the colourist, they lack the rippling effect of light which was captured in the famous broken brushstroke of Impressionist oil painting. The point is made in the exhibition by the small selection of oil paintings which punctuates it.

These include some fine and unfamiliar ones from lesserknown collections. There is a sumptuous twilight scene, Towing a Boat, Honfleur (1864), from the Memorial Art Gallery of the University of Rochester and a beautiful View of Rouen (1872), a classic 1870s painting in muted lavender tones, from a private collection.

What is striking, though, is how Monet's pastel and oil techniques converge in his images of the Thames at the beginning of the 20th century.

Holed up in a hotel room over-looking Waterloo Bridge, Monet began working in pastel while waiting for his canvases to arrive, and the smeared technique he adopted when he switched to oil means that it is not easy to distinguish between the two media.

Perhaps the flattening effect of the atmospheric conditions in fogbound London helped bring about this change in Monet's approach to painting.

Some of these Thames studies come to the brink of abstraction, as do Monet's famous last subject, the water-lilies.

Some of the pencil studies for these, a loose configuration of looped pencil lines scrawling across the paper, might almost be mistaken for a kind of Surrealist automatic drawing, but are actually an old master's self-devised shorthand memo to himself.

n The Unknown Monet is at the Royal Academy, London, until June 10. Admission: Adults £8 (concessions: £7 over 60s/disabled, £6 students, £3 12-18 years, £3 income support, £2 8-11 years, 7 and under free). Until April 20 you can also see Citizens and Kings: Portraiture in the Age of Revolution 1760-1830, a spectacular exhibition of era-defining portraits of monarchs, politicians and leading citizens from Europe and North America by artists including Goya, David, Reynolds and Gainsborough.