This proposal aims at deepening understanding the complex discoloration issue of emerald green and Scheele’s green paints (hereafter called “EM” and “SH”, respectively) affecting late 19th c.-early 20th c. oil paintings. µ-XRF mapping and µ-XANES spectroscopy at S K-, Cu K- and As K-edges will be exploited to perform a spatially resolved study of EM and SH oil paint systems before and after exposure to controlled conditions of light, humidity and temperature. Such analyses will permit to define how the pigment formulation, the binding medium and environmental agents trigger EM and SH degradation processes.