A rare, rediscovered watercolor by JMW Turner could fetch a cool half-a-million when it hits the auction block at Christie’s New York next month. The foggy watercolor sketch of the Venetian lagoon was identified as being by the 19th-century English Romantic painter when it was submitted to Christie’s “Request an Estimate” digital appraisal service. It had previously be falsely attributed to the Victorian art critic and artist John Ruskin.

This discovery was unexpected windfall for the artwork’s owner, since the new attribution to an artist as renowned as Turner has inflated the painting’s price tag by around 10 times. The Approach to Venice or Venice from the Lagoon (c. 1840) will appear in Christie’s Old Master and British Drawings sale in New York on February 4. It has an estimate of $300,000–$500,000.

The work’s current owner is a descendant of the engineer Haddon C. Adams, a known Ruskin obsessive who once said, “collecting Ruskin is my one luxury.” Though he was born in England in 1898, Adams immigrated to Illinois after graduating from Cambridge University in 1922 and eventually became the U.S. ministry of transport’s chief bridge engineer. He bought the Turner watercolor around 1930 and it has remained in the family ever since.

At the time that Adams bought the work, it had been correctly attributed to Turner but was misidentified later, according to a report in The Art Newspaper. Ruskin is known to have been a passionate admirer of Turner’s, once declaring: “We have had, living with us, and painting for us, the greatest painter of all time, a man whose supremacy of power no intellect of past ages can be put in comparison for a moment.” This rave review may explain Adams’s interest in acquiring a Turner.

Joseph Mallord William Turner, Self portrait, age 24 (ca. 1754). Photo: Universal History Archive / Getty Images.

When the painting’s owner submitted a photograph of the artwork to Christie’s online appraisal service, it immediately piqued the interest of British drawings and watercolors specialist Rosie Jarvie. “The image was poor, and the painting was behind old glass, which had a greenish tint,” she told TAN. Nonetheless, she “had an instinct, from the strong brushstrokes, economy of line and the palette, that we really needed to see this properly.”

The Turner specialist Peter Bower was able provide evidence for this hunch when he studied the paper on which the watercolor has been made and found that its type matched that of other views of Venice by Turner. Expert Ian Warrell has also given the reattribution his seal of approval.

Some watercolors by Turner have been known to fetch over $1 million, though others command smaller sums. Last year, another of his long-lost watercolors was rediscovered. The owner had acquired it within a larger group of paintings for which they paid just £100, or roughly £235 ($299) in today’s money, at a small regional auction in 1990.

The artwork, titled The Entrance to Bishop Vaughn’s Chapel, St David’s Cathedral, Wales (1795) was painted when the artist was just 20 years old. It sold at Cheffins auction house in Cambridge for £37,000 ($47,025) over a high estimate of £30,000 ($38,000).