A new cleaning method for historic stained glass windows

Historical stained glass has a clear tendency to form a crusted layer on its surface due to the environmental exposure. One of the most delicate aspects to be faced during the restoration of historic glass windows is the cleaning of these thick corrosion crusts.For several centuries, stained glass windows have been cleaned using damaging mechanical (scalpel) and chemical (high acidic or alkaline solutions) methods. Today's understanding of the cleaning process comprises two complementary aims: improving the readability of the glass and reducing the weathering process of the historical glass. The act of removing deposits and encrustations resulting from corrosion should not endanger the artwork itself. Mechanical methods, cleaning solutions or gel pads are now being developed. However, these methods could present further problems.In this study, we examine a new cleaning method that can be employed to remove encrustations in a quick and efficient way. Results up to now, obtained on specific stained glass windows are promising; further researches are in process for other cases. We propose an optimized solution to dissolve calcium carbonates and lead sulphates from Avila Cathedral glass windows crust. This system is tailored to control pH, temperature, conductivity and concentration of Ca2+. Continuous on-line analysis of these parameters allows us to monitor the cleaning process. In particular, the Ca2+ concentration in the cleaning solution is controlled by means of a Ca2+ ion selective analyzer.