I was loitering on the ground floor of the National Portrait Gallery waiting for the doors of the National Gallery to open when I discovered a display on the ground floor devoted to work inspired by the long-standing friendship between Ishbel Myerscough and Chantal Joffe.   I hadn’t known that they knew one another or that they were at Glasgow School of Art together.   I found it oddly powerful to see the way the work of two very different artists interrelates, each one painting themselves alone and together, with children and from behind, totally different in technique, but touching in the way they depict themselves.