Portugal presents a rich collection of stained glass windows from the 15th to 20th centuries. This project involves the rediscovering of the old technologies in the art of stained glass painting, the investigation of the historical evolution of the different painting materials through critical analysis of historical written sources and the reproduction of historical recipes. These reproductions allow us to evaluate their technology (powdering treatment, sieving, and annealing temperature and time), as well as to determine the influence of environmental agents (humidity, rain, aerosols, pollution and environmental temperature fluctuations) in their corrosion. This study enables the evaluation of the best conservation procedures and strategies to prevent further degradation.