A painting once attributed to French modernist Fernand Léger has now been determined to be a fake. The work long-languished out of view in the Guggenheim collection under suspicion that it was not "right." It took today's latest scientific analysis to uncover miniscule traces of Cold War-era nuclear bombs in the fabric of the canvas to confrim that the work was made after Léger's death.

American art collector Peggy Gugenheim had purchased the work as a Léger dating from 1913-1914. In the 1970s, scholar Douglas Cooper voiced his doubts about the work's authenticity. The Solomon R. Guggenheim Foundation tucked the piece away.

Italian Institute for Nuclear Physics (INFN) was recently enlisted to examine the painting. They used a particle accelerator to assess the level of carbon 14 in an unpainted edge of the canvas. The cotton in the canvas had a concentration of carbon 14, the radioactive variation of carbon, consistent with the post-World War II era, when nuclear bomb testing altered ratios.

"After 1955 the level of radiocarbon in the atmosphere, and thus in living organisms, almost doubled in about 10 years," Pier Andrea Mandò, head of the Florence division of the INFN, said in a statement.

"It is due to this rapid change that works from those years can be dated extremely accurately," Mandò explained. "In this case, it has allowed us to discover that the canvas support could not have been produced before 1959. The work cannot therefore be one of Léger's original series of Contrastes de forms. Nor is it a later copy by the artist, since Léger died in 1955."