MALDI-MSI: A new method for studying the degradation of historical organic pigments

Abstract

The aim of the thesis is to study the light degradation process of eosin using the Matrix Assisted Laser Desorption Ionization - Mass Spectrometry Imaging (MALDI - MSI). Geranium lake is an organic red pigment based on eosin, used by Von Gogh and his contemporaries. In order to study its behavior, a sun-light aging treatment was performed on oil-based samples of Geranium lake in a range of time of 40 days. The samples were created in the laboratory to recreate the paintings used by artists of the time. The preliminary analyses were conducted on the pure pigments synthetized in the laboratory by Attenuated Total Reflection Infrared (ATR-IR), X-ray Powder Diffraction (XRPD) and Positive Electrospray Ionization Time-of-flight Mass Spectroscopy (TOF-MS-ES+) and monitored by non-invasive analysis, Fiber Optic Reflectance Spectroscopy (FORS) and microscopic analyses. The main challenge of this project was the optimization of the sample preparation prior MALDI-MSI analysis. The results obtained provide innovative spatial information. Within each cross section, it is possible to obtain the lateral distribution of the key molecule, eosin, the secondary products related to its degradation process and any third molecules related to the interaction between the different components of the paint, oil, lead white and eosin. Studying the spatial results of all the samples collected during the ageing process provided us with new information on the behavior and distribution of this pigment over time.