Photoacoustic Analysis of Natural Indigo, Palygorskite and Synthetic Maya Blue

Maya blue is an organic / inorganic pigment which is composed principally by two elements: a white clay known as palygorskite (in the Mayan dialect Sakalum), and a blue dye called indigo, this dye is extracted from the plant Indigofera suffruticosa . The mixture and the warming of these two elements produce the Maya blue, which exhibits unusual features such as: resistance to the assault of the acids in warm or high temperatures, his persistent color in spite of having been exposed to different climatic conditions as a result of the passage of time and the specific chemical composition that this pigment presents. In the present investigation natural indigo, palygorskite and synthetic maya blue were analyzed with a new implementation technique called photoacoustic analysis, which detects the structural changes that happen in the material under a controlled increase of temperature. Due to the fact that this technology detects with clarity where the structural changes happen but not that type of changes happen, it used as base termogravimetric analysis. One of the important findings, it was that in the spectrum of the synthetic maya blue were detected the structural changes of the clay and the dye, something that with other used technologies had not been achieved to observe.