Throughout the US, coal mines abandoned before environmental laws produce acid mine drainage, a soup of toxins that can turn contaminated streams as acidic as lemon juice. One of the main byproducts of acid mine drainage, ferric oxyhydroxides, also happen to be the base for commercial red and yellow paints. Guy Riefler, a professor of environmental engineering at Ohio University, has invented a method for collecting the iron sludge in the runoff and converting it into pigments. With the help of artist John Sabraw, Riefler is tweaking his process with an eye to eventually manufacturing commercially viable paints. There's certainly no shortage of raw materials: a single seep near Ohio University oozes out enough sludge to produce one ton of pigments every day.
Via Smithsonian Magazine.