The Frenchman who taught Lowry how to paint matchstick men

For decades they have hung in the homes of art lovers across northern England, their true value scarcely even guessed at by their owners.

Meanwhile sale prices of works by Adolphe Valette, the French impressionist who taught LS Lowry to draw his celebrated matchstick men and workaday mill worker scenes, have soared.

This month two new exhibitions open marking the artist's talent at capturing the dark satanic beauty of Edwardian Manchester. Among the items on show at the Lowry Gallery in Salford will be nine paintings and sketches donated by private collectors who answered a public appeal to scour their homes, attics and storerooms for previously unseen works by Valette. The discoveries include a preparatory sketch of a lost work, possibly entitled Les Baigneuses (Bathers), and a large painting, Femme L'Avant, whose owner said it had not been displayed since 1934.

While Lowry has become one of Britain's most bankable artists – his Piccadilly Circus belonging to the late hotel tycoon Lord Forte is expected to fetch a record £6m when it is sold at Christie's later this year – the former master has continued to languish in relative obscurity outside Manchester. But the lives and talents of the two men were critically entwined and now the teacher is attracting renewed interest from collectors who also admire the work of his most famous protégé.

Both men arrived at the Manchester School of Art in 1905. Lowry, then aged 18, was little more than a Sunday painter while Valette brought a whiff of glamour and the exoticism of the Impressionist movement that was set to sweep the world before it. Lowry studied under the Frenchman for a decade – assiduously learning the drawing techniques in his life classes.

It is not known why Valette chose to come to Manchester, but like Lowry he saw the austere beauty of the city's smoggy streets. Among the subjects he chose were tug boats on the Manchester Ship Canal and the fog-shrouded red-brick Victorian architecture.

Bill Clark, who is holding the largest ever sale of Valette's work, with 24 on display at his gallery in Hale, said large canvases depicting urban life could fetch up to £50,000. Some were bought by amateur collectors in the 1970s for as little as £40.

Valette retired due to ill health and returned to France in 1928. He died during the Nazi occupation in 1942. Today the Manchester Art Gallery has nine of his paintings on display. Cécilia Lyon, curator of the Lowry exhibition, said the public response to its appeal had helped to increase the knowledge of the artist. "I am delighted that local people have been able to be a part of the exhibition," she said.