Stability of zircon pigments in water and diethylene glycol media: The case of turquoise V–ZrSiO4

The stability of pigment particles can be affected by physico-chemical interactions between the pigment particles and a solvent. In this study, the surface charges and stabilities of blue V–ZrSiO4 pigments in aqueous (water) and non-aqueous (diethylene glycol) suspensions were investigated. As a function of pH, the isoelectric points (IEP) for the commercial and synthesised pigments were determined to be 2.2 and 1.7, respectively. ICP-OES results show that the cations of V–ZrSiO4 pigments dissolve in both aqueous and non-aqueous systems. The dissolution of the pigment particles was more significant in DEG because the total ion concentration (>2000 ppm) was higher than that of the aqueous medium (>200 ppm). The colour stability of the V–ZrSiO4 powder deteriorates as a consequence of an insufficient chemical stability both in the water and DEG media. Additionally, the V–ZrSiO4 particles dissolve with proton-promoted and hydroxyl-promoted dissolution mechanisms in the aqueous medium, whereas these particles dissolve with a ligand-promoted dissolution mechanism in the non-aqueous medium.