Overcoming obstacles in the Raman analysis of art objects

Raman analysis has played an important role in the conservation and authentication of art objects. Raman is very specific where each molecule has a “fingerprint” signature in the middle infrared region of the electromagnetic spectrum (4000-400 cm-1), where the Raman analysis result lies. Importantly, the Raman also yields results in the far infrared region of the spectrum (<600 cm-1). In this region inorganic based pigment manifest a unique spectral response. Unfortunately, there are obstacles inherent in the Raman data collection that complicate the analysis. For example, some objects can be very large AND have areas of interest that are very small. Additionally, these areas of interest can exhibit interfering fluorescence, which can obscure the desired Raman signal. For example, in considering an indigo dye as applied to parchment paper, both the dye AND the paper exhibit strong fluorescence. Examples will be presented showing the application of shifted-excitation Raman spectroscopy to mitigate this fluorescence as well as the application of silver colloid in very small quantities to further reduce the fluorescence interference.