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From the photos it appears that the artist waterproofed an apartment in an abandoned building and filled it with 80 kL of hot, saturated copper(II) sulfate (solfato di rame) solution. As the solution cooled, copper(II) sulfate pentahydrate crystallized on every surface in the room. I thought this was timely since I was playing around with copper(II) sulfate today. I dissolved it in water and added sodium carbonate to precipitate copper(II) carbonate. Then I mixed that with excess carbon and heated it in a crucible to smelt metallic copper. Maybe I'll get out the oxygen torch tomorrow and see if I can make silver from that big jar of silver chloride waste in my hood.
More photos can be found here and here.