Auguste Rodin’s The Man with the Key has turned pale green over the past century. But despite the uniform color, several different copper-containing minerals have engulfed the bronze sculpture as it corroded in the acid rains and pollution of Oslo where it is displayed. Researchers at the Norwegian University of Science and Technology are now working to pick out whether certain areas have formed antlerite or brochantite, which are both green minerals that form as copper oxidizes but are treated differently when conservationists try to preserve bronze sculptures. The researchers used hyperspectral infrared imaging to compare the spectra from patches of the sculpture to the spectra of just antlerite and just brochantite. The researchers then created maps (bottom row, from left: visible appearance of sculpture, brochantite map, antlerite map) that show areas where each mineral is most present (dark areas indicated with arrows).
To read more about this material, check out the story by Bethany Halford.
Credit: City of Oslo Art Collection and J. Spectral Imaging
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