More over-heated gush has been written about the Greek-American singer Maria Callas than about any other performer, with the possible exception of Greta Garbo. Given that Callas’s centenary has just occurred (2 December), we can expect much more of the same. Steven Knight is shooting a biopic, Maria, with Angelina Jolie, which one hopes will fare better than Franco Zeffirelli’s cringe-making version, Callas Forever (2002), which starred the unfortunate Fanny Ardant. Exhibitions in Milan and London have been dwarfed by the opening of a museum dedicated to the diva in Greece. A rather creepy sounding holographic concert is touring the world, following on from the exceedingly creepy Marina Abramovic’s 7 Deaths of Maria Callas, which has also been doing the rounds. All of which is operatic music to the ears of Warner Classics, for which she is still a major earner.