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"The brown paint samples contained a large number of chrome atoms of a specific chemical type. And these were different from the chrome atoms originally found in the paint (the identified atoms all contain three extra electrons). What is noticeable is that we also identified a great deal of barium and sulphur close to this ''reduced'' chrome. This probably comes from barium sulphate, a colourless filler which was mixed with the paint. This leads us to suspect that the addition of barium sulphate could be the source of the discolouration,"Dr Joris Dik, involved in the research on behalf of TU Delft, explains.
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