Turner collection set to make £15m at Sotheby's auction

The most important collection of watercolours by JMW Turner to go on sale for more than a century is to be auctioned in July.

Collectors will have a rare chance to bid for 14 works spanning more than four decades of Turner's life, including a watercolour produced when he was 73.

The collection, to be sold at Sotheby's on 5 July, is estimated to fetch up to £15m. The sale comes a year after another Turner watercolour, The Blue Rigi, depicting Lake Lucerne, was sold for a record £5.8m.

The auction has caused a stir in the art world because it is the finest collection of watercolours to be sold since the 1870s, two decades after the artist's death. Henry Wemyss, head of British watercolours at Sotheby's, said: "The 14 watercolours embrace almost every aspect of Turner's achievements."

Among the works are landscapes and seascapes, including sublime views of the Swiss Alps, which Turner visited often, a view of Venice and a painting of Waterloo shortly after the battle, as well as scenes of Scarborough and Hastings.

Lundgernzee, a painting believed to have created three years before Turner's death in 1851, is expected to fetch up to £3m and is one of the most "extraordinary works" in the collection, according to Mr Wemyss.

"It's a large watercolour with a lake right in the middle and a moon above the lake, with cattle, a donkey and figures in the foreground. It is the most extraordinary impressionistic image and is quite surprising to have been done by an old man. We know he was creating his later works in his studio under candlelight, not doing it on the spot in the Swiss Alps, although he had amassed a lot of sketches from his visits there earlier in his life," he said.

Mr Wemyss said the later work laid the foundations for the Impressionist movement led by Monet and Pissarro, yet his earliest watercolours, painted as a 29-year-old, were very different in style. "The young Turner's landscapes were looking for sublime views. They were not Impressionistic, and colouring such as greens, blues and greys were more sombre and fashionable at the time," he said.

Turner was born in 1775 to a wigmaker and barber who displayed his son's work in his shop. He entered the Royal Academy of Art when he was only 17, after Sir Joshua Reynolds, who was president of the Royal Academy, admitted him.

The artist showed an initial interest in architecture but was advised to stick to painting. A watercolour of Turner's was accepted for the Summer Exhibition of 1790 after only one year's study. Although renowned for his oils, Turner is considered to be one of the greatest masters of British watercolour landscapes and is often referred to as "the painter of light".

The collection, put together over two decades by the Belgian entrepreneur Baron Guy Ullens, will be on display at the auction house's galleries today.