Artist Robert Rauschenberg’s radical objective was to operate “in the gap between art and life”. His work crossed boundaries, pioneering combinations of media and genres. 11 years after his death in 2008, this remorselessly innovative figure remains a strong creative influence, especially on young artists. But before his fame became global, one of Rauschenberg's first solo exhibitions took place in Florence in 1953. British writer and art historian Martin Holman tells the story.