Alteration processes of medieval stained glass windows. Study and protection treatments

The anxiety caused by the fast growing decay of historical stained glass windows as a consequence of increasing environmental pollution, encouraged institutions of several countries To sponsor a series of scientific works aimed both to slow down this fast forwarding deterioration and to develop repair and preservation methods. After an initial review of the chemical composition of the stained glass windows and of the differences depending on historical epochs and origins, a discussion about chemical attack mechanisms, degradation processes and formation of superficial crusts opens lip. Finally, the methodology used in their cleaning and restoration is briefly exposed and some criteria on the still polemic question of treatments for protection are commented.