Immaculate image that emerged from the gloom: Dalya Alberge reports on how two brothers' belief that they had found a work by Velazquez paid off

AS SOON as a canvas with an image of The Immaculate Conception (left) had been cleaned, experts saw the light: a Velazquez had emerged from layers of discoloured varnish and dirt.

The idea of discovering a painting by the 17th-century Spanish master had seemed too good to be true: the last Velazquez to come on to the market was nearly a quarter of a century ago.

As Sotheby's put it yesterday, in unveiling their pounds 6m painting, it is 'one of the most exciting art discoveries in recent times'.

No wonder then that when they were approached by a Paris dealer convinced that he had the real thing, they took the unusual step of encouraging him to have it cleaned. Auction houses generally like dirty pictures to remain dirty for the sale, leaving restoration to the buyers.

The man who made the initial discovery is Charles Bailly, a French dealer, who purchased it from Ader Tajan, the Paris auction house, in 1990. It was catalogued as 'circle of' Velazquez. Mr Bailly, backing a hunch, ignored the estimate of a mere pounds 40,000, buying it for pounds 2.1m. He said: 'When my brother and I saw the painting for the first time, we were convinced it was a masterpiece and the chance of a lifetime. Before the sale, we spent days and nights studying all the works of Velazquez.'

The picture was cleaned over three months by Zahira Veliz, a Velazquez specialist. She said: 'The technique of this youthful work is entirely consistent with the methods found in Velazquez's known paintings of the Sevillian period.'

She pointed to evidence of Velazquez's 'footsteps', as she put it: there was, for example, the use of smalt in the sky, and underlying brushstrokes in the background where the painter had cleaned his brush - particularly evident in X-ray photographs. Comparisons with another image of The Immaculate Conception in the National Gallery, London, show close stylistic similarities: both pictures show how the artist prepared his design with little underdrawing.

The painting has been dated to 1619, when the artist was working in Seville, and before his move to Madrid in 1623, where he became Court Painter. The Sotheby's image reflects his interest in naturalistic representation and his play with the effects of bright light. Like the National Gallery picture, and The Adoration of the Magi in the Prado, Madrid, the figure is a portrait of a real person rather than an idealised religious image.

Hugh Brigstocke, head of the Old Masters department at Sotheby's, suggested that the pounds 6m estimate is conservative: he explained that the pounds 2.3m fetched by a Velazquez in 1970 represents about pounds 20m now. The painting, which will be sent on a world- wide tour for prospective buyers, will be offered for sale on 6 July.

(Photograph omitted)