Leading article: A genuine fake

News that the Courtauld Institute of Art may rule that what for the last 50 years has been considered a top-quality fake by one of the world's most brilliant forgers is, in fact, an authentic 17th-century work – by an obscure artist – raises fascinating questions about what determines the value of an art work.

The Courtauld was never under the illusion that "The Procuress" was a real Vermeer. Anthony Blunt, the then director who was later revealed as another fake of sorts, accepted the donation believing it to be the work of the forger Hans van Meegeren. The conclusion that it dates from the 17th century, not the 1930s, ought to mean its value soaring. But such is the mystique surrounding Van Meegeren that his fake Vermeers retain a certain cachet and value, and whether this work remains interesting to collectors once revealed to be the work of "an artist" is unclear. It is perhaps time to reassess the whole notion of authenticity.