Facile Synthesis of Three Kobolds: Introducing Students to the Structure of Pigments and Their Characterization

Thénard’s blue (CoAl2O4), Rinman’s green (CoZnO2), and Berzelius’ red (CoMgO2) are pigments that have been used from the 19th century in works of art. Their synthesis can be conducted by a very simple and rapid method: by ignition of a wafer of dried filter paper soaked first in a Co2+ solution and then subsequently soaked in a partner salt (Al3+, Zn2+, or Mg2+) solution. Through their following characterization using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM), the students can be introduced to further concepts, protocols for sample preparation, and data interpretation regarding these mainstream characterization techniques. Although originally designed for first-year undergraduates, this activity can be tailored to match different levels and can be used as a part of STEAM (science, technology, engineering, arts, and mathematics) activities in middle/high school and general public outreach.