Vibrational spectroscopy and SEM-EDX analysis of wall painted surfaces, Orchha Fort, India

Any alteration of pigments due to environmental degradation leads to the disfigurement of the depictions and change in hue and saturation that artists intended to represent through paintings. An analytical characterisation of pigments of early 16th century Orchha fort has been attempted through non-invasive micro-Raman and results corroborated with FTIR and SEM-EDX. The analysis revealed the formation of calcium oxalate on painted surfaces due to biological colonisation that led to deterioration and sometimes masking of pigment layer. Analysis demonstrated the transformation of calcium sulphate dihydrate to low-temperature anhydrite in exposed white painted areas made from mixtures of gypsum, calcite and lead carbonate. The black colour on paintings is due to biological colonisation on the red outer surface layer and not by the use of black pigment. Lapis lazuli for blue, copper based pigment for green, yellow ochre for yellow was found used in decorations.