The French manufacture of Sèvres, famous for its production of fine porcelain artefacts, has been synthesizing pink pigments mainly composed of the spinel phase ZnAl 2−x Cr x O 4 with x varying from 0.25 to 0.41 since the middle of the 19 th century. This kind of pigment is mixed with an uncolored frit to obtain decorations for porcelain artefacts. However, the pink color of 2 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 at the Cr K-edge measurements showed that the new formed phase belongs to the same spinel phase ZnAl 2−x Cr x O 4 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.