The stability of gahnite doped with chromium pigments in glazes from the French manufacture of Sèvres

Abstract

The French manufacture of Sèvres, famous for its production of fine porcelain artifacts, has been synthesizing pink pigments mainly composed of the spinel phase ZnAl2−xCrxO4 with x varying from 0.25 to 0.41 since the middle of the 19th century. This kind of pigment is mixed with an uncolored frit to obtain decorations for porcelain artifacts. However, the pink color of the pigment is altered in a particular uncolored frit and a brownish color appears. The mechanism of this color change was investigated. Observations under a scanning electron microscope revealed the formation of a phase rich in Cr resulting from reactions between the uncolored frit and the pigment during firing. X‐ray diffraction combined with Rietveld refinements and X‐ray absorption near edge structure measurements at the Cr K‐edge showed that the new formed phase belongs to the same spinel phase ZnAl2−xCrxO4 than the pigment, but with a higher Cr content x. We showed that its formation and thus the stability of the pigment is driven by the Al content in the uncolored frit.