Nothing could have prepared the art world for the astounding moment in 1970 when, at a Christie’s sale on 27 November, the world auction record for a painting smashed through the million-pound barrier for the very first time. It was Velázquez’s portrait of his assistant Juan de Pareja, and in the week leading up to its sale the international press became excited about the possibility that it would beat the previous record of £821,482, paid in 1961.