A campaign is under way to uncover Alexander Runciman’s lost mural of the Ascension, a masterpiece of the late 1700s painted over in St Patrick's church, Edinburgh

The place they’re calling Scotland’s Sistine Chapel doesn’t look like a Catholic church at all. And for good reason: because when St Patrick’s, a handsome, “square-style” church just off Edinburgh’s Royal Mile, first opened it was Episcopalian. The year was 1774: its name in those days was St Paul’s, and Scotland’s Protestant churches were already in the fractious state that defined them for centuries.

So much so that when its ministers commissioned a series of paintings for the ceiling above the altar, they decided they should be based on stories that hit home the message that theirs was the “true” faith: Jesus and the woman at the well, the return of the prodigal son, and Moses and Elijah.

Pride of place, though, went to a large mural of Christ’s Ascension. The artist was Alexander Runciman, who was born in Edinburgh and studied in Glasgow before being apprenticed to a landscape painter, and working on stage sets. In 1767 he and his brother, John, went to Rome. John died in Italy, but Alexander remained there for five years and became acquainted with the work of the Renaissance greats as well as contemporary artists. On his return to Britain he exhibited at the Royal Academy and settled in Edinburgh, painting among other pieces a series of subjects from the Gaelic legendary figure Ossian at Penicuik House in Midlothian.