‘It was magical’: hidden self-portrait by English artist Norman Cornish found at museum

An unseen self-portrait of one of the most popular northern English artists of his generation has been discovered hidden on the back of another painting.

The discovery of a new work by Norman Cornish – arguably the most famous artist to emerge from the north-east of England in the 20th century – was made during preparations for a big show of works by him and another titan of northern art, LS Lowry.

The exhibition, at the Bowes Museum in Barnard Castle, County Durham, aims to celebrate the two artists as “extraordinary storytellers of everyday life” in northern England.

The self-portrait was discovered a month ago by the Bowes Museum conservator, Jon Old, who was working on Cornish’s painting Bar Scene , from the collection of Durham county council.

Old said that Bar Scene had an unusual backboard set into its stretcher. Puzzled, he decided to remove it. “To my surprise it revealed this wonderful other painting on the reverse, which was quite magical.”

He said he felt “very privileged to have been the first person since Norman Cornish to see this self-portrait”.

Vicky Sturrs, the Bowes’s director of programmes and collections, recalled a colleague “belting down the corridor saying ‘Jon’s found a painting’!”

“It is so exciting and shows why conservation is so important,” she said. “It’s not just about caring for objects, it’s about finding out more – and that’s why this discovery is so incredibly special. I think we all now might be hovering around Jon when he does conservation.”

Both paintings, front and back, will be on display, although it does mean one will have to be upside down at various points of the day.

The self-portrait is clearly from Cornish’s younger days, and while it is rough and ready it does have a raw power to it.

“I love it,” said Sturrs. “The immediacy of it just speaks to me and I love the brush, being able to see the way that has gone on.”

The exhibition includes more than 50 paintings, sketches and drawings by Lowry and Cornish side by side.

The painters both depicted working-class northern life, but were different in a number of ways.

Lowry, a rent collector from a middle-class background, was an outsider looking in while Cornish, a miner for 33 years, was very much an insider – he was painting his people, said Sturrs.

The notion that Cornish, who died in 2014, was just about painting flat-capped working-class men drinking pints, or families queueing for the chippy, is disabused by a number of works.

One with an arresting edge to it is entitled Crucifixion (1960) , a watercolour of a crucified miner on a telegraph pole, painted on a page from the Radio Times. It expresses how Cornish felt about the treatment of miners – how he felt they were treated like enslaved people and spoken to like convicts.

Another painting, of his wife, Sarah, peeling a potato, is regarded by his family as a “pitman’s Madonna”.

The exhibition will show, Sturrs hopes, how the two artists, who knew and respected each other, were “on a par” – which raises questions of why Lowry is so much better known and more highly regarded than Cornish today. There are, for example, no Cornish works in the Tate collection.

Hannah Fox, the executive director of the Bowes, said she hoped the show might go some way to redressing the balance.

“Norman’s work should be seen as important as Lowry’s and should be more widely recognised. It is in the north east. Everybody knows Norman Cornish. So we want to make sure everyone else does.”

• Kith and Kinship: Norman Cornish and LS Lowry is at the Bowes Museum from 20 July until 19 January