[58] Clarke, 2011, The Medieval Painter’s Materials and Techniques: The Montpellier Liber Diversarum Arcium, p. 105 (§1.5.1A eng., char of willow and vine), 251 (§1.5.1, lat.), 174 (reference to nigrum optimum). See also Reissland, 2014, Why do Artists Prefer Vine or Willow Charcoal?