The American artist Spencer Tunick has been photographing huge voluntary nude crowds since the 1990s.
Previous locations have been as diverse as a glacier to the Sydney Opera House.
Recently he began working in colour for the first time, photographing his first scene of painted nudes at the Big Chill Festival at the UK.
Mark spoke to him about this latest phase of work.
click Watch a video of Spencer's work at the Big Chill
First broadcast August 4th 2010.