* Andy Warhol's Oxidations series, begun in 1977, in which he invited friends to urinate onto a canvas of metallic copper pigments, so that the uric acid would oxidize into abstract patterns ;

* Andy Warhol's Oxidations series, begun in 1977, in which he invited friends to urinate onto a canvas of metallic copper pigments, so that the uric acid would oxidize into abstract patterns ;

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