
Invisible Art: In the eye of the beholder? —
An exhibition of "invisible" artworks by artists including Andy Warhol, Yves Klein and Yoko Ono has gone on display in London. The show features Roman Ondak's "More Silent Than Ever" (2006), an empty room with a hidden eavesdropping device.

Invisible Art: In the eye of the beholder? —
"Magic Ink" by Gianni Motti (1989) is made up of a series of drawings, sketched in invisible ink, which were visible for a brief instant before disappearing.

Invisible Art: In the eye of the beholder? —
To creat "Untitled (A Curse)" (1992), artist Tom Friedman hired a practising witch to cast a curse in the space above this empty plinth.

Invisible Art: In the eye of the beholder? —
Bruno Jakob has spent the past 25 years making invisible paintings, including those shown here, by exposing a primed canvas to the "energy" of a person, animal or environment.

Invisible Art: In the eye of the beholder? —
Teresa Margolles' installation "Aire/Air" (2003) consists of two air conditioning systems that spread a fine mist of droplets of water previously used to wash the bodies of murder victims in Mexico City, before they were autopsied.

Invisible Art: In the eye of the beholder? —
"Invisible: Art about the Unseen, 1957 - 2012" is on at the Hayward Gallery in London, from 12 June until 5 August, 2012.