Kapoor appeals for protest in support of Ai Weiwei
For the past five weeks there's been no sight of Ai Weiwei, the Chinese artist and human rights activist who was detained by security staff at Beijing Airport.
His continued detention has prompted a global appeal by the sculptor Anish Kapoor, who wants museums and art galleries throughout the world to close for one day in protest.
He has also dedicated his latest work to Ai Weiwei.
Will Gompertz reports.