After about 1817 Constable, for aesthetic and financial reasons and with an eye to professional advancement, determined to create large-scale paintings which could compete with those of contemporaries such as JMW Turner. X-rays show that Constable originally had in mind a completely different scene on this six-foot preparatory sketch, a view of Dedham Vale probably made in his London studio from earlier Suffolk sketches.

The view is from the south bank of the Stour, looking back across the river just below Flatford. The barge on the left has taken on board the white horse and is about to set off to reach a spot downstream where the tow path resumes on the opposite bank. Just beyond the barge is a small island called ‘The Spong’. Willy Lott’s house is just visible to the left centre in the middle distance. Following the exhibition of this work, Constable was elected an Associate of the Royal Academy.

Stratford St Mary is two miles west of Flatford and was the site of a picturesque timberframed watermill, partly visible on the left. The viewpoint is from a footbridge across the river.

Constable first explored this subject, it seems, in a small plein air sketch of 1811. This full-scale sketch, once doubted as to its authenticity, differs from the finished painting mainly in the area with the young anglers in the lower centre. The sketch is also a more lively, even agitated, image than the calmer exhibited work. The forms are described with a free brushwork.

The true subject of this painting is the beautiful scenery of the Stour Valley, with its limpid river and richly wooded banks and meadows under a cloudy sky. Although it was well-received, the painting did not sell at exhibition. Constable worked on it later on a number of occasions. Some criticism of its sky led him to make a famous statement about his beliefs: ‘That Landscape painter who does not make his skies a very material part of his composition – neglects to avail himself of one of his greatest aids…the sky is…the chief "Organ of sentiment"…’

This vertical oil sketch on paper relates closely to the left hand side of The Hay Wain and includes the motif of the dog on the bank. Willy Lott was an old tenant farmer and Constable used the image of his cottage throughout his career.

Constable has extended the viewpoint in the earlier sketch (above) to include here most of the cottage which appears in The Hay Wain 1821.

Constable made this drawing around 1809-11. The rowing boat is apparently moored by the edge of the river bank close to the brick parapet at the back of the Mill House at Flatford. The boat was later introduced by him in the same position on the right-hand side of The Hay Wain 1821. Constable’s early outdoor studies were to provide a valuable resource when he was working on his large compositions in the studio some years later. This same boat, for example, appears not only in The White Horse 1819, but also in Salisbury Cathedral from the Meadows 1831.

This small sketch in oil on paper was probably made in Constable’s London studio. It contains nearly all the principal elements of the finished painting, including the cart fording the stream. It also includes a barge with raised sail in the distance which is absent from the exhibited picture, although traces of a sail in a different position can be seen in x-rays of the painting.

This loosely painted full-size sketch includes a figure on horseback not present in the finished painting (below), although they were originally transferred to the exhibition version and then later painted out. Constable has also omitted the central chimney on the cottage. His main aim seems to have been to quickly define the main elements of his composition and the overall patterns of light and shade. The brown under-painting shows through in various areas.

The view is taken from below his father’s mill at Flatford with Willy Lott’s house to the left. A hay wagon crosses the stream and turns across the main channel of the shallow or ‘flat’ ford. A woman bends to gather water, a dog walks along the bank and an angler walks through reeds on the right. In the meadows beyond workers are cutting hay.

Constable’s original title was Landscape: Noon and it was painted more quickly than usual for the Royal Academy exhibition where it did not sell. The work was greatly admired by French artists when shown at the Paris Salon in 1824.

Constable probably began work on this image in a rented London studio in autumn 1821.

This full-size sketch seems to have been based on three small pencil studies of 1814. There is a new emphasis on the commercial vessels on the Stour after the more pastoral views of the previous few years.

A remarkable x-ray, which shows the many alterations to the sketch he made, can be seen in an interactive digital display in the final room of the exhibition.

What looks like a square well-head with a bell on a chain in the bottom left corner may be connected with a self-levelling system for locks.

The major alteration from the full-size sketch is the addition of another barge in the centre of the composition, together with a lighterman poling it towards mid-stream. He is given a white shirt and red cap which make him stand out conspicuously.

Constable told John Fisher in 1822 that these changes were intended to give the painting ‘a rich centre’. This also led him to exclude the man rowing in the skiff on the left and the two boys fishing on the right, among many other more minor changes. The painting was exhibited with The Hay Wain 1821 in Paris in 1824 and was very well received.

The view is of the lower gate of Flatford Lock looking west toward Dedham Church. A barge waits in the flooded lock chamber, steadied by a man pulling firmly on a line passed round a bollard. In the centre a man in a red waistcoat heaves on a crowbar to work the lock mechanism.

The format of the painting is unusual in being vertical rather than horizontal, no doubt to emphasise the activity of the central figure. Constable added strips to the top side of his sketch’s canvas when he decided to adopt this format. The main forms are boldly laid out with a palette knife.

This finished version follows the full-size sketch fairly closely, although the brushwork is far more restrained. Constable was pleased with the work, which he told John Fisher ‘is a good subject and an admirable instance of the picturesque’. The critics agreed and indeed the painting sold on the opening day of the Academy exhibition. Constable wrote to Fisher that the picture had ‘the light of nature… The language of the heart is the only one that is universal’. He believed his apparent idiosyncrasies achieved ‘lightness and brightness…the essence of landscape’.