Oil painting of Charles I's children is actually an 18th century print

• The portrait was on display beneath a staircase in Norfolk’s Oxburgh Estate
• Historians believed it to be an oil painting by Sir Anthony van Dyck 
• When it was sent away for treatment a conservator realised it was a rare print

A portrait of Charles I’s children that was hidden in a dark corner of a National Trust property and believed to be a painting is in fact an 18th century print.

The portrait titled Three Eldest Children of Charles I was on display beneath the staircase in Oxburgh Estate in Norfolk and viewed by thousands of visitors each year.

Historians always believed it to be an oil painting by Sir Anthony van Dyck.

But when the artwork was sent away for treatment at the National Trust’s Royal Oak Conservation Studio at Knole House in Kent, a conservator realised it was in fact a rare print by Jacob Christoff Le Blon, the 18th century painter who pioneered the three-colour printing process.

National Trust curator Jane Eade said van Dyck’s portrait was ‘much copied’ but ‘only three Le Blon prints of it were known to survive’.

‘To have a discovered a fourth is really exciting, especially as it is the only version that remains hanging in its historic setting,’ she said.

The portrait titled Three Eldest Children of Charles I is on display at Oxburgh Hall in Norfolk and viewed by thousands of visitors each year

Historians always believed it to be an oil painting by Sir Anthony van Dyck

The artwork was sent away for treatment at the National Trust ‘s Royal Oak Conservation Studio at Knole House in Kent (pictured) when it was discovered to be a rare print by Jacob Christoff Le Blon

Le Blon was a German-born painter and engraver who died in 1741 aged 73.

He was the first to create a three-colour printing process – the forerunner of the colour printing used today which involves four colours (cyan, magenta, yellow and key).

Le Blon’s revolutionary method used mezzotint – a monochrome printmaking process – with separate plates inked in blue, yellow and red and superimposed on one another in order to create an endlessly variable depth of hue.

Until then, artists had inked colours one beside the other on a single printing plate.

A specialist paper conservator at the Royal Oak Conservation Studio helped identify the colours Le Blon is known to have used, such as indigo and carmine or red lake.

Ms Eade said that a ‘thick layer of 19th century varnish was particularly challenging’ but that the conservator was ‘able to gently clean the surface layer, thinning the varnish in places and smoothing cracks to improve the picture’s appearance’.

The canvas backing was peeling in some places but, since it was likely to be the original backing used by Le Blon’s Picture Office, it was repaired and conserved rather than replaced.

The print will be on display at Oxburgh Hall (pictured), the home of the Bedingfeld family who were royalists and devout Catholics

Le Blon moved to London in 1718 where, calling himself James Christopher, he was granted a royal privilege by George I to practice his trichromatic printing.

Royal patronage gave him access to Kensington Palace to copy paintings – including the Van Dyck of Charles I’s children.

It is not known for certain how and when the print came to Oxburgh Hall, the home of the Bedingfeld family who were royalists and devout Catholics.

But the discovery suggested they were secret Jacobites – supporters of the Catholic Stuart royal family in exile instead of George I.

The portrait includes the future James II, the last Catholic monarch of Britain, whose son James Francis Edward Stuart attempted to take back the throne after the failed Jacobite rising of 1715 – six years before Le Blon copied van Dyck’s original portrait.

Ilana van Dort, Oxburgh collections and house manager, said: ‘There is now evidence that Henry Arundell-Bedingfeld was a secret Jacobite and van Dyck’s portrayal of the children of Charles I, including the future James II the last Catholic monarch of Britain, would have great resonance and symbolism.

‘Copies of this painting are known to have been popular with those sympathetic to the Jacobite cause and it would have been quite feasible that the print has spent its whole life at Oxburgh, although we lack enough evidence to prove it.’

The print will be on display at Oxburgh Hall alongside some 16th century textile fragments and the story of its conservation will be featured in the new BBC Two series Hidden Treasures of the National Trust.

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