A Victorian medium guided by the dead was an unlikely pioneer of modernism

The Tate’s vast extension is high on good intentions, but low on excitement. It’s all a bit too polite

Abstraction is back, and female artists are in the vanguard of the revival

Maria Merian’s 17th-century butterfly pictures are both stunning natural history and proof of a deep spirituality

We don’t need a £260m pyramid, says our art critic. We need a creative force like the Impressionists to break the grip of the art establishment