The masterpiece used as a dartboard

For centuries they have languished in the shadows – unseen, unloved and unappreciated. Now a new exhibition is shedding light on some of Britain's lost art treasures. Arifa Akbar tells their extraordinary stories

They are medieval icons, Renaissance masterpieces and Enlightenment paintings. Yet they have languished in store-cupboards or hung in dusty corners of the country's most provincial museums. Some have been damaged, others have been left unappreciated in dusty cabinets, and allowed to quietly decay. One of them was even used as a dartboard.

But now, after centuries in the dark and cold, a team of art experts has brought a staggering collection of previously-neglected works back into the artistic canon.

Today, after years of extensive research, these works will be unveiled at the National Gallery – allowing the British public to finally appreciate their full, historic importance.

The resultant exhibition boasts a relatively humdrum name: Discoveries: New Research into British Collections. Yet it is the culmination of an extraordinary research project by a crack team of 25 art detectives, who spent three years scouring the country in search of "buried" art treasure.

In their attempt to locate and identify around 8,000 paintings, they visited some of the country's smallest galleries, and trawled through long-forgotten, obscure collections. The resulting exhibition highlights eight works – the most important historical discoveries they made – which were created over a period of nearly 500 years.

But that is not all. Behind the scenes, the entire range of the archivists' findings will form the backbone of an online database designed to explain the impact of the rediscovered works. Dr Nancy Ireson, the exhibition's curator, says that the importance of some insights should not be underestimated.

The project was partly conceived, she explains, because small regional art galleries were increasingly unable to employ their own research staff, and so their collections were "losing knowledge" about a painting's wider context or provenance.

"This project is about art treasures, and paintings hidden away in stores, unnoticed by many, despite representing a huge part of Europe's art heritage," she says. "A regional museum often has one curator, and space enough to show only part of its collection, what is most relevant to the regional's audience. It's only when we sent in a dedicated team that these stories were found."

Discoveries: New Research into British Collections, until the 10 February 2008, www.nationalgallery.org.uk

Architectural Fantasy with Classical Ruins

By Giovanni Paolo Panini

Although this fantasy scene (1729-30) was long displayed at the Northampton Museum and Art Gallery, no one had been sure in which year it was created. When researcher Pablo Perez D'Ors began to investigate its subject matter, however, he found that he was able to verify an exact date for the painting's execution.

Although the neoclassical Panini was renowned for his architecturally fantastical vistas, the freestanding column that appears in this work is a real piece of "ephemeral architecture" built in the Piazza Navona, Rome, in 1729, for an extravagant firework display to celebrate the birth of the king of France's son. The column was a temporary installation, and was probably made from papier mâché. Panini would have been commissioned by the king to represent the celebratory scene, and this suggests the artist was a greater proponent of realism than might have been realised.

Until now, the "fantasy" was regarded as an imaginary landscape of Roman ruins. "Now we are able to say that this is an imaginary painting with a twist," says D'Ors. Two other paintings by Panini of this same installation hang in the Louvre and in Dublin.

The Barricad at Porte Saint -Denis

Nicholas-Edward Gabe

This iconic image of a young woman mounting the barricades was painted in 1848. It was long believed to be an allegory of liberty, epitomising the fiery spirit of the French Revolution at its tumultuous height. At least, that is how the painting was billed at the Bowes Museum in County Durham.

After tracing the identity of the "revolutionary", researchers found that she is no allegory but an actual figure who took part in a local protest at Porte Saint-Denis. The subject came to a sad end; having climbed on to the barricade on 23 June 1848, she was only able to wave a flag, briefly, before falling victim to government gunfire. In the painting, she's standing on an overturned carriage, a detail corroborated by several eyewitnesses.

Nancy Ireson, the exhibition's curator, said researchers began to question the accepted view of the painting after realising that it was done in June rather than February 1848, so linking it to local unrest. "The woman is waving a flag over the threatened closure of a workshop, not because she's the personification of liberty."

The Death of Cleopatra

Benedetto Gennari

This 1686 erotic depiction of a naked Cleopatra in the throes of death – with her back arched and blood dripping from her bosom – was one of the most popular images at the Victoria Art Gallery in Bath. Yet the visionary behind this portrait was Benedetto Gennari, an Italian painter better known for conservative religious paintings.

Those more familiar with his canvases would have associated Gennari with works he undertook for the wife to King Charles II, a devout Catholic. It was only when a researcher came across an certificate on the back of this work that she connected the artist to Sir Francis Gwyn, a politician and womaniser.

It transpires that the painting was given to Sir Francis as a tactical gift by Gennari, in the hope of pleasing the lothario with its female sensuality.

What could have persuaded such a painter to create such an erotic image? Money, explains the National Gallery's Nancy Ireson. "Gennari had been promised a stipend by Charles II, which didn't materialise. Knowing Sir Francis worked in Charles II's treasury, Gennari painted this to earn his admiration, hoping he would get his stipend from the King."

Gennari worked in vain. he never got the stipend.

The Holy Family

Gianfrancesco Maineri

The Holy Family (c1500) is one of four works that Maineri produced of the same subject. Traditionally, it was seen as a straightforward biblical illustration – but after curators began re-examining the work, they realised it carried an idiosyncratic series of hidden meanings.

Nancy Ireson, who was charged with unpicking the perplexing range of imagery, says that the glass sphere the child cradles (suggestive of an orb) may have been intended to prompt thoughts of Christ as an imperious figure.

Meanwhile, the translucent veil held by the Virgin may suggest the " veil of flesh", which refers to Christ's physical humanity concealing his divinity. The eagle on the pilaster could relate to the Este family, at whose court Maineri enjoyed considerable success.

"Now people have begun to really look at the work, and started to ask many more questions," she adds. "There are so many more layers of meaning than we had thought it to have."

Courtyard at the Rubenshuis

Attributed to Anton Gunther Gheringh

Until the 1980s, this rare portrait of the artist Peter Paul Ruben's home in Antwerp, executed between 1645 and 1675, was left hanging in a hallway at the Denham Court youth detention centre in Buckinghamshire, where inmates used it as a makeshift dartboard.

That was until Buckingham County Museum, which had put the work in storage after the detention centre closed, realised it was an early depiction of the famous building.

Anne Cowe, the archivist who rediscovered the work – which, as the "before" picture shows, was heavily pockmarked and covered in holes and slash-marks, thanks to its former life – says her investigations served to overturn received wisdom on what Rubens's home (restored in the 19th century) may have looked like.

The frescos on the exterior of the building, designed by Rubens, had never before been illustrated in colour (art historians had only found Rubens's sketches of them). It had been supposed that the images between the upper and lower-floor windows had been created in marble.

"We had no idea what these frescos looked like before this painting was identified as 'Rubenshuis'. Its value in terms of scholarly revelations is immense and exciting," says Cowe. Scholars from Rubenshuis, now a gallery housing much of Rubens's work, will visit the National Gallery next week to examine the work.

The Ark on Mount Ararat

Filippo Palizzi

For many years, this was one of Falmouth Art Gallery's most-viewed paintings, mainly on account of the highly realistic depiction by Palizzi (1818-99) of the animals and of the recognisable biblical scene of Noah and his Ark. Yet, in spite of its popularity, the gallery had scant information to help them gain a greater understanding of The Ark on Mount Ararat's wider relevance.

Then a researcher, the art historian Anne Cowe, began to look into the origins of the painting. She identified a very similar work by the same artist, albeit almost twice its size, in the Museo del Capodimonte in Naples.

While investigating the larger sister image, Cowe discovered that it had been commissioned by Vittorio Emanuele II, the first king of Italy. Meanwhile, analysis of Palizzi's surviving records revealed that the two works were indeed closely related to each other; the artist had used the one to develop the subject matter of the other.

Art experts have since come to regard the Falmouth version as a preliminary study for the canvas now in Naples, and it has also been linked to two other preparatory works by Palizzi, both of which are in private hands.

The Death of Seneca

Luca Giordano

The death of Seneca, the philosopher and adviser to the Roman Emperor Nero, who was accused of plotting to kill his leader, was a subject that had been of enduring interest to Giordano, the influential Italian master, who repeatedly painted the moment at which Seneca committed suicide.

However, until very recently this detailed work, painted between 1650 and 1675, was listed as "attributed to" Giordano. It was only when a researcher, Malcolm Barclay, deciphered the artist's discreet signature on one corner of the canvas and examined the stylistic elements in the work in more detail that it could be confirmed as Giordano's creation.

Because of the uncertainty over its provenance, the masterpiece had been locked away in storage by curators at Bolton Museum and Art Gallery, and had never been part of any major publication on the work of the Neapolitan artist. The museum has since managed to gain the funds to restore and re-exhibit the work.

Nancy Ireson said it was the stylistic analysis that finally confirmed the painter's identity. "Giordano did many versions of Seneca's death, and what the researcher found was that this was a reverse image to the one the painter had done that now hangs in the Louvre in Paris."