Derby Museum has revealed that a painting that was for years thought to be a poor replica by a follower of the English painter Joseph Wright (1734-1797) could be authentic, and worth in the region of £1million.

Coliseum by Moonlight, believed to be painted by Wright after he went on a Grand Tour of Italy in the 1780s, was identified when the conservator working on another Wright painting of the same subject realised that the museum inventory listed two paintings of the Coliseum by Wright. There was disbelief, Lucy Bamford, senior curator of art told the BBC, because the only possible fit for the mystery painting was one in the storeroom that was ‘absolutely terrible’.

However, upon closer investigation they saw that the painting had been the victim of bad restoration work in the 1960s. The museum says that they will use solvents to remove the botched over-painting, and use infrared technology to find out more about the original, a process which is estamated to take approximately a year.

Bamford said that they still needed to be cautious: “We have no way of knowing for sure, even with the modern analytical techniques, what sort of state Wright’s original painting of the Colosseum by Moonlight will be in. Other paintings restored around the 1950s/60s have been discovered to have been sanded and scrubbed so as to give a smooth surface on which the restorer could lay new paint. Conservation science was in its infancy, and a favoured approach was often to simply paint over the existing picture so as to ‘improve’ the appearance of it and make it ‘displayable.’

The painting will be on public view mid-way through the restoration process, as part of an exhibition about the Grand Tour scheduled for the summer.