One of my favourite pictures in the National Gallery was painted some time around 1470 by an unknown artist in Swabia, in oil on silver fir. It shows a woman about whom we know only what the inscription at the top left of the picture tells us: that she was a 'geborene Hoferin', born into the Hofer family. The calm expression of her pale, smooth features as she looks into the distance, and the beginnings of a slight smile, add to the tease of anonymity. So, even more, do the meticulous details which give the picture its individuality - the great billow of her ruched head-dress with its fine pinning and needlework, and its train which falls to the right shoulder, then leads across the front of the sitter's dark dress to disappear over her left shoulder; the precise rendering of the clasps on her dress, and of the zig-zag thread or lace fastening the collar at her throat; her right hand, with two rings on the little finger, across her heart; her left holding a sprig of forget-me-not delicately between forefinger and thumb. And there, towards the top of the coif, invisible to the woman but clear in every detail to the viewer, poses a single fly, casting the slightest of shadows. It is tempting to consider the fly as a reminder of mortality, as the text on the wall by the picture suggests it could be, though there is also the possibility that it might just be ...