The National Portrait Gallery has purchased a self-portrait by the late Craigie Aitchison, complete with slashes that the artist inflicted on it after an acquaintance described it as “flattering”. This comes in the wake of a two-year sentence handed down to Wlodzimierz Umaniec, who defaced a Rothko at Tate Modern as a means of publicising his Yellowist ideology. Now, since the painting was Aitchison’s own work and property, no charges were levelled when he indulged in his own bout of practical self-criticism, but one does wonder whether his amendments have added to or detracted from the monetary value of the piece. Also, taking into account Duchamp’s desecration of the Mona Lisa and the Chapman brothers having their wicked way with Goya, it must be asked whether there’s some sort of hierarchy at work. If a more exalted artist than Mr Umaniec were to whip out the felt tips and improve an existing work, would there be a different reaction. An Aitchison slashed by Aitchison costs £36,512; how much for an Aitchison slashed by Rothko?