zaffre

noun2

1. •
   Cobalt oxide obtained by roasting cobalt ore, used as a blue pigment.

   • If Zaffre or Regulus of Cobalt be dissolved in the same manner in spirit of nitre, or aqua fortis, a reddish colour is produced on exposing the paper to heat. — 1791
2. •
   A cobalt blue colour, like that of the pigment.