It had travelled from Italy to the upper Dales, perhaps via London, and may have been the work of not one but two old Masters.
William Soper had paid just half a crown, or 12½p, for what he considered an attractive watercolour of the Doge’s Palace and St Mark’s Square in Venice, at the house clearance sale of a local vicar at the end of the war.
The scribble on the back set it apart, as did the cropping that had been done to the canvas.
But for decades it was nothing more than a wall decoration in a suburban house in Leeds.
Yet now, it has emerged as perhaps the only example of an unknown work by one sought-after artist to have been defaced by another one.
Mr Soper, a garage man from Chapel Allerton, who collected Chinese porcelain in his spare time, had been led by an art dealer friend to the dispersal sale of the well-connected Rev Trevor Basil Woodd, who lived at Outershaw Hall, near Buckden.
“It was 1945 and the war was still on,” said his son, Bob. “He left with a load of pictures under his arm. I was there myself – I was eight.”
Mr Soper Jr, who acquired the painting following his father’s death, had long thought that it may be the work of the 18th century English landscape artist John Sell Cotman, a leading member of the so-called Norwich School. It appeared to be Cotman’s scribble on the back.
But research has now pointed to the writing having been added when Cotman was a student of the London arts patron, Dr. Thomas Monro – who was also psychiatrist to George III.
“The issue is that Cotman only overpainted a tiny corner of it. I believe the rest was done by someone else,” Mr Soper said.
He thinks the base painting may be the work of the contemporary Italian artist Canaletto, who specialised in views of Venice, Rome and London, and whose work was collected by Dr Monro.
“My research suggests that this was one of the Canalettos Dr Monro had bought,” said Mr Soper, a retired engineer who now has the picture in a conservatory at his home in Wetherby.
The doctor was famous for mentoring young artists – JMW Turner, as well as Cotman, was in his circle – and Mr Soper believes his picture may have been defaced by the young Cotman when he was set a challenge of copying it.
“It would have been sacrilege, but Cotman was then a country bumpkin, down from Norwich. As a 17-year-old he probably just doodled over it.”
He added: “If that is the case, this would be unique – the only known Canaletto from the Monro collection.”
A mint Canaletto would fetch around £¼m today. A work of his defaced by Cotman, possibly more. However, Mr Cotman acknowledges that the truth may never be known.
“My research indicates that it may be the work of Canaletto, or his nephew, Bernardo Bellotto. Whether the art establishment will see it that way is another matter.”
The link from a London art circle to a clergyman in the Dales is his father, the collector and wine merchant Charles Henry Lardner Woodd. He was a personal friend of John Ruskin, the leading art critic of the Victorian era, who had links to Cotman.
Mr Soper, 83, hopes now to gather wider views.
He said: “I would like this resolved once and for all, and the only ones who can do so are the experts at our great museums and galleries.”