Restored Gainsborough painting on show at National Portrait Gallery

A Thomas Gainsborough portrait of his nephew has had more than a century’s worth of yellowing varnish removed revealing just why one friend of the artist described it as “more like the work of God than man”.

A conservator at the National Portrait Gallery has cleaned the 1773 portrait of Gainsborough Dupont, and the result has been a revelation. Dupont, the gallery said, looks less the son of a humble Suffolk carpenter and more a gilded youth who could have stepped straight from the court of Charles I.

The results were revealed on Monday ahead of the oval portrait’s display as part of the gallery’s exhibition, Gainsborough’s Family Album, opening to the public on Thursday.

Polly Saltmarsh, a conservator at the gallery, said it was a joy to work so closely with paintings. “Having the opportunity to study the techniques Gainsborough has employed in this beautiful portrait has been a highlight of the preparation for the forthcoming exhibition.

“Removing the old varnish and revealing elements which were previously obscured is very satisfying, and witnessing the reaction of curators and visitors seeing the painting after treatment is a real pleasure.”

The portrait was identified as Dupont, Gainsborough’s nephew and apprentice, in 2003 by the art historian Susan Sloman.

Philip Thicknesse, a close friend of Gainsborough, had eulogised the work calling it “the finest head he ever painted” and “more like the work of God than man”.

Gainsborough gave the painting away and soon afterwards it entered the collection of Lord Bateman, an aristocrat with connections at court, and it hung at his Park Lane residence.

For the past 100 years it has hung at Waddesdon Manor, the grand Rothschild house near Aylesbury, Buckinghamshire, which is run by the National Trust.

Conservators discovered that the painting had undergone previous conservation work, probably in the 19th century. The canvas and paint layers were in a stable condition but it was compromised by an old degraded varnish which had yellowed with age.

Removing it revealed how Gainsborough included touches of blue in the sitter’s hair and around his eyes, reflecting the gorgeous blue of his jacket.

• Gainsborough’s Family Album is at the National Portrait Gallery in London from 22 November to 3 February