Called Also Rugerus Theophilus (Theophilus, Called Also Rugerus)

• 
  via
  On Divers Arts: The Foremost Medieval Treatise on Painting, Glassmaking, and Metalwork
  by Called Also Rugerus Theophilus
  Softcover, Dover Pubns, ISBN 0486237842 (0-486-23784-2)