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The picture shows the alchemist trying to produce the elusive Philosopher's stone, which could turn ordinary metal into gold, but instead, to his amazement, he discovers phosphorus. However, Wright does not picture the alchemist in a 17th-century background but he romanticises the room by imagining medieval gothic arches and high, pointed windows as if he is in a church. He also gave a very favourable impression of the actual process which involves the reduction by boiling of urine. A 1730 description of the manufacture of phosphorus described the need for 50 or 60 pails of urine that was both putrid and "bred worms".