An exhibition of paintings containing human ashes by controversial Czech artist Roman Tyc has raised eyebrows after opening Tuesday in a gallery in Prague's historic city centre. "When you're six and your mum dies, you see her as a metal urn and know her only from photographs for the rest of your life, you believe there's a way to free her from the can," reads an introduction to the exhibition, written by Tyc. "It's Tyc's personal testimony. His mum died when he was six, and he's trying to cope with her death," Edmund Cucka, director at the Dvorak Sec Contemporary art gallery, told AFP at the opening of the exhibition, dubbed "Grave Robber". The 37-year-old Tyc created 19 portraits, using the grey ashes to create silhouette faces contrasting against a black background. "The portraits are clean, there's nothing shocking," said Cucka, adding human ashes had been used as material by artists on Czech soil in the 1960s. Cucka said the portraits "are not specific people like actors or something. They are people he chose -- he was interested in their stories." Cucka declined to disclose the origin of the ashes when asked by AFP. The artist, who claims that excess ashes from funeral homes end up in waste dumps, was not present at the opening of the exhibition. "He said maybe he'd come and maybe not. He's very nervous. He's definitely not here right now," said Cucka. The gallery said the paintings were not for sale, and that it had asked the artist to scatter the ashes in a dignified place with all due piety after the exhibition. Tyc is a member of the Ztohoven group of controversial artists who gained fame in 2007 after pirating a public television broadcast and superimposing images of a nuclear explosion on footage of a beauty spot. In the same year, Tyc replaced the standard "Walk" and "Don't Walk" symbols of little men on 50 traffic lights in Prague with ones jumping or urinating, earning him top prize at a Vienna art festival and a month in a Czech prison.