£1m art treasure found in Aberdeen gallery

Now Aberdeen Art Gallery has discovered that the triptych, which has been in storage for many decades, is a work by a 15th-century Italian master that could be worth up to 1 million.

Only when a veteran curator put the overlooked artwork on show to fill an empty display case and a Renaissance art expert with a few hours to kill in Aberdeen chanced across it did the truth emerge.

Christie's specialist Francis Russell identified it immediately as the work of Sienese sculptor and painter, Il Vecchietta, dating to about 1450.

Speaking for the first time about the find, Russell said: "In one second, I knew it was Siena, in five seconds I knew it was almost certainly by Vecchietta, and in ten seconds I convinced myself it was."

Three other leading experts have now confirmed his opinion and the Madonna Of Humility – bequeathed to the gallery 115 years ago by Miss Georgina Forbes as the work of an unknown artist – is now seen as a major new asset for a collection better known for contemporary art.

The gold-painted triptych will be loaned this month to the Arts of Siena, an exhibition in the Tuscan city, where officials are delighted by the find, before returning in style to Aberdeen.

Aberdeen Art Gallery's lead curator Jennifer Melville, who first put the unattributed picture on display, said the Vecchietta was a surprising and welcome addition to the gallery's assets.

"It ranks very highly in our collection," she said. "It is very, very unusual for this to happen. It was one of the first things to come into the collection. It's very intimate and very sweet but to my knowledge it was in store virtually all the time."

The triptych comprises three hinged panels. In the centre is the Virgin Mary, her crown held by two angels, with Christ on the cross in the gable above; St Francis and St Dominic are in the wings.

It was bought in the early 1890s by Georgina Forbes, and her older sister Frances, who came from a well-connected and wealthy strand of the Forbes family in north-east Scotland. They were the daughters of Lt Col Arthur Forbes, who was related to the Barons of Craigievar.

They lived in Aberdeen, but spent their winters in a flat in Via San Niccolo, Florence, from where they ventured out to purchase art. The triptych carries a label "to be given on my death and my sisters' to the new Picture Gallery at Aberdeen. Georgina E Forbes. Florence, October 1885."

Georgina Forbes died 10 years later and, as promised, the picture went to the gallery on Frances's death in 1899.

Aberdeen, like most public collections, does not sell paintings. But such a work, though they rarely reach the private market, would be worth at least in the high six figures, and probably close to the 1m mark, Russell and other experts say.

He stumbled across the work while visiting relatives in Aberdeen and taking a quick detour to check out the gallery's collections.

Partly because the triptych was never shown or restored, it is "remarkably well preserved", Russell said. He added that every detail of the picture showed it as "a characteristic (Vecchietta] work, presumably dating from soon after 1450 by the most versatile Sienese artist of the period."

The find has brought predictions that there are other vintage masterpieces in Scottish art collections just waiting to be identified. The Public Catalogue Foundation, a charity that is painstakingly photographing and cataloguing oil paintings in public art collections in Britain, has recently begun work in Scotland.

It expects to publish 13 volumes, covering an estimated 30,000 paintings in Scottish collections, with work already well under way in Glasgow, and experts beginning work in Dundee, Aberdeen, and northern Scotland.

PCF chairman Fred Hohler said: "It's inevitable that re-attributions and new discoveries will be made. Over 90 per cent of the national collection on average is never shown. Most of us don't have the faintest idea what these paintings look like."