Self Portrait, by Gwen John, Tate Gallery London

With her hair is parted in the middle the artist’s gaze is direct but withdrawn as if holding the secret of her inner life intact. The painting glows from within like a dark room lit only by firelight. A brown shawl is half-slipping off her shoulders: a brilliant device that adds movement to a composition which may otherwise be too stiff.

The whole image is held together by an interplay between restraint and freedom. A locket is held in place at her throat by a narrow, black ribbon.

Perhaps this is a memento of her mother, who died when Gwen was only eight years old and may have contributed to the quietness and intensity within this image of herself.

Gwen and her brother Augustus John grew up in Tenby in Wales. Augustus’s celebrity was such that he was briefly acclaimed as the leader of British post-impressionism, then celebrated as the pre-eminent portrait-painter of his age. And while recognition came slower to Gwen, the singularity of her vision, drawing on early expressionism and abstraction, as well as her own mystic embrace of Catholicism, earned her a significant place in modernist art and she is now the more famous John.

However, Augustus- always the harshest critic of his own work, and the most loyal supporter of his sister’s- once prophesied that in 50 years, he would be known “as the brother of Gwen John”.