Raman spectroscopy on the identification of the organic mordant used in gilding decoration of Persian archaeological tiles

Several organic reference materials including gums, proteins and oils, as well as the organic mordant used for adhering gold leaf on ten archaeological Persian gilded tiles dated from the fourteenth to the sixteenth century were studied by Raman spectroscopy. The relative surface area under the spectral components of the C-H stretching region from the reference materials and archaeological samples were used as criteria for identifying the class of the organic material used as mordant. Our studies showed that a drying oil has most probably been used as mordant in the archaeological samples. Also, the possibility of the use of gum ammoniac as gilding mordant is considered.