Stained glass windows are fascinating for many reasons – their delicate combination of light and substance, the beauty of the colours, the contrasts. In the shadow of the bright and colourful glass parts, the metal cames mostly receive few considerations. Yet they play an essential role in the graphic language of stained glass windows, highlighted forms, but also being the structure skeleton of these objects. In addition to that, the cames carry precious information about the technology and the history of each stained glass window. This case study focuses on actively corroding lead alloy cames from two stained glass panels, on permanent museum display. The purpose was to understand the origins and mechanisms of the corrosion.