Art review The crushing power of Wales's great modern artist

This is Gwen John straight, no chaser.

- Jonathan Jones

From far left: Girl in a Blue Dress, The Pilgrim and Mere Poussepin Seated at a Table

(BY PERMISSION OF AMGUEDDFA CYMRU - MUSEUM WALES; YALE CENTER FOR BRITISH ART, PAUL MELLON COLLECTION/ GWEN JOHN)

Cardiff's National Museum has put together a superb, daunting retrospective of the woman who is now, perhaps, the most famous Welsh artist.

It is not a blow-by-blow biographical story of how she was born in Haverfordwest in 1876, how she and her brother Augustus both loved art as children, how she insisted on going to the Slade like him then made her life in bohemian France. Instead, the moment you enter the show, you are plunged into her spiritual, austere existence. We meet her in the glory of her solitude, painting cats and the sparse rooms she rented in Paris and women alone in moments of calm thought.

There is a row of variants of a young woman in a blue dress with long dark hair sitting weakly in an armchair, a table at her elbow, all painted in about 1920. In most there's a cup and teapot on the table, in one it's a bowl of soup. She looks down as she reads a letter, occasionally a book. Their titles vary too - The Letter, The Seated Woman, The Convalescent.