The red shades of synthetic red and violet dyes composed of linear quinacridones that are made from terephthalic acid. Quinacridone dyes can exist in four crystalline allotropes, two of which are sold as red and violet pigments. Although synthesized in 1896, quinacridone colors were first recognized as useful pigments and marketed by DuPont in the 1950s under the name Monastral. They are lightfast colorants used in paints, printing inks, and plastics.
