Post-sale clean reveals painting to be work by teenage Turner

A stormy landscape by JMW Turner was rediscovered after 150 years when his signature was revealed during post-auction cleaning.

- Harriet Sherwood

The Rising Squall, Hot Wells, from St Vincent's Rock, Bristol, is one of the artist's earliest works - he was just 17 at the time.

When the oil painting was sold last year it was attributed to a "follower of Julius Caesar Ibbetson", an 18th-century artist. Dreweatts, the auctioneers, had suggested the work would fetch £600-800 but the buyer is believed to have paid less.

Now, in a year of exhibitions and events to mark the 250th anniversary of the birth of the man widely considered Britain's greatest artist, the painting is to be sold again.

This time it will be auctioned by Sotheby's on 2 July with an estimated value of £200,000-£300,000. "We are as certain as it's possible to be that this painting is by Turner," said Julian Gascoigne of Sotheby's.