Chemical degradation and mineralogical transformations on based lime blue pigment

The aim of the study is to explain the process of chemical degradation in short times of the ultramarine blue pigment [Na₃Ca(AlSi₃O₁₂)S] when used mixed with lime in a highly basic environment for applications on the outside of stone supports or mortars. For the study, mixtures were produced with only lime and commercial ultramarine blue and also with the red pigment based on ferric oxide (hematite). The mixtures were studied and analysed by optical microscopy and Raman to define the transformations of the original crystalline phases into any new secondary phases.