The design criteria involved the selection of chromophores
and counterions utilizable by the ceramic industry
for their chemical and technological features (and cost).
The chromophores are those currently used to impart
colour to Zr- or Ti-bearing pigments, such as rutile (i.e. Cr,
Mn, Ni, V) or zircon and baddeleyite (i.e. Fe, Pr, V).
Furthermore, Co was chosen for its well-known colouring
capacity