Tate Britain’s Thomas Gainsborough exhibition reveals an artist of enormous skill and prodigious talents. Famed for the elegance of his portraits, he also pioneered a new approach to landscape which had a powerful evocation of mood that prefigured the Romantic Movement.

He was one of many artists who benefited from the increasing interest in art emerging in the wake of Britain’s growing economic and political pre-eminence, and his work is a striking record of the sensibilities prevalent in Britain in the latter part of the 18th century. Many of these characteristics are exemplified in “The Linley Sisters”, his masterpiece of 1771-72.

“The Linley Sisters” is a double portrait of Elizabeth and Mary, the daughters of Thomas Linley, a music professor and director of concerts in Bath. Gainsborough was a keen, self-taught amateur and was close friends with Johann Sebastian Bach and Carl Friedrich Abel. He became acquainted with the Linleys when he moved to Bath in 1760 and in his portrait of Elizabeth and Mary his love of female beauty, nature and music all combine seamlessly.

Elizabeth and Mary Linley were highly accomplished sopranos who performed frequently at public concerts in London, Bath and other provincial towns. Elizabeth, in particular, was something of a celebrity. Her beauty and the expressive sweetness of her voice enraptured her audience, so much so that, when she sang in Oxford in 1772, she reportedly induced in the young men a “sort of contagious delirium”. We recognise the reaction provoked by pop stars today.

Her younger sister Mary was equally talented and she joined Elizabeth from 1771 as a singer at oratorios, festivals and concerts. Gainsborough locates the girls - aged 18 and 14 respectively - in a spring woodland setting, romantically surrounded by shady trees and foliage, with a clump of wild primroses blooming on the bank by Mary’s side.

An affinity with nature was regarded as the hallmark of a person of refinement and the representation of the Linleys in harmony with nature was a conscious, poetic expression of the new 18th-century cult of sensibility.

Gainsborough poses the sisters as if they are taking a break during an informal, al fresco concert. This impression was, of course, a fiction as both the figures and the landscape were painted in the studio. But Gainsborough’s ability to integrate his sitters with their settings almost persuades us that the scene may have actually taken place and the atmospheric portrayal of the landscape represents a radical new development. This effect was enhanced through the judicious use of overlapping colours, elimination of hard outlines, and the subtle deployment of half-tones and combinations of light and shadow to suggest form.

The sisters themselves present a striking contrast. Mary, the more vivacious of the pair, is alert and animated, engaging the viewer with her confidence and impish grin. The more introspective Elizabeth stands slightly behind her, staring abstractedly out of the picture. Her air of preoccupation may have been intended to suggest a mind rapt in the contemplation of nature, but equally it may have been a reference to the personal crisis she was facing at the time.

During the period in which the portrait was painted she had become the subject of a scandal involving a broken engagement and rumours of a liaison with another man. Before the portrait was completed she had eloped with Richard Brinsley Sheridan, the playwright and future politician - an impending drama which may well have been playing on her mind.

As for Mary, the directness of her gaze would have certainly been seen as unconventional. Modesty was a prized feminine virtue and it was not considered appropriate for a woman - especially an unmarried woman - to look directly into the eyes of a man to whom she was unrelated, even if that man was a portrait painter. Mary’s direct engagement with the viewer may have been permissible because of her youth, but it was nevertheless extremely unusual in portraits of this period.

Unlike many other artists, Gainsborough strove to capture a true-to-life likeness of his sitters. Contemporaries often marvelled at the accuracy of his portraits. He was also unusual in painting all the parts of the portrait himself. It was common practice during the 18th century for artists to employ assistants to fill in the drapery and elements of the background.

Sir Joshua Reynolds, who was Gainsborough’s great rival, retained a large retinue of studio hands for this purpose. Gainsborough, however, realised that the lesser parts of the canvas were as significant to the final effect as the face and helped to ensure a unified composition. This unity was further enhanced by his technique of painting in a darkened half-light, which not only allowed him to perceive the general masses of the face and figure, but also helped to achieve the rich chiaroscuro characteristic of his work.

Perhaps the most innovative aspect of Gainsborough’s technique was his use of “odd scratches and marks”, which appear almost abstract when viewed up close but resolve into a recognisable image when viewed at a distance. This technique can be seen in the Linleys’ dresses, particularly in details such as the lace sleeves and parts of the skirts, and in areas of the background. It was highly individual and represents an approach that seems extremely modern, even today.

Joanna Banham is head of public programmes at Tate Britain Thomas Gainsborough runs until January 19 2003, at Tate Britain, London. It includes more than 250 works from British and American collections and charts the development of Gainsborough’s career from the 1740s to his death in 1782. For more information call Tate Britain Schools LiaisonTel: 020 7887 8767Tate Ticketing: 020 7887 8767Admission: pound;8.50Schools concession: pound;3 per student for pre-booked groupswww.tate.org.uk

TEACHING TIPS

General consideration

What does the painting tell us about the people?

What do the surroundings, costume and accessories tell us about their personalities, status and occupation?

Why was the portrait made? Was it for posterity or propaganda?

What was the artist’s relationship with the sitters?

Specific investigation

How does the painting compare with other contemporary portraits, especially paintings by Joshua Reynolds?

Examine the different techniques. How were these achieved? What was their function?

How life-like is the portrait and its landscape?

How have colour and shadow been used to blend the sitters with their background?

How does the artist convey the sitters’ personalities?

What does the portrait say about the status and role of women in the 18th century?

Lesson ideas

* Make a portrait showing the sitter in a landscape rather than in an interior. What difference does it make to the mood of the portrait?

* Which sections of the painting seem the most realistic? Are there any parts that look less convincing?

* If you were to be painted by a famous artist, how could the painting show the kind of person you are? Where would you sit and what would you want with you? What would you wear and where would you look?

* How do colours enhance the mood of the painting?

* Many of Gainsborough’s landscapes were created in the studio using still lifes of twigs for trees, broken mirrors for water and broccoli for foliage. Collect some of these materials and arrange them to form your own miniature landscape.