This is Cologne Cathedral, Germany’s biggest and home to an abundance of colourful treasure.ULRIKE BRINKMANN, ART HISTORIAN and HEAD OF STAINED GLASS CONSERVATION STUDIO, COLOGNE CATHEDRAL: “ Glass painting is a key element in European Gothic architecture. Less stone is used in the construction of the walls and the spaces are filled with stained glass. These windows show many figures and parables, which held symbolic value for the faithful. When one looks at them you see how the churchgoer felt surrounded and protected by the saints and the precious material adds to the aura.” However the art historian says that these priceless European artworks have a hidden, fragile character. ULRIKE BRINKMANN, ART HISTORIAN HEAD OF STAINED GLASS CONSERVATION STUDIO, COLOGNE CATHEDRAL: “ Glass from the Middle Ages until the late 15th century present their own problems because of their special makeup they use the materials of the time, not at all like today´s glass. The glass is attacked by moisture as well as other harmful substances.” Ulrike works in a team of 13 to restore the glass to its former glory. The glass itself , pollution and sometimes previous conservation techniques all work against the restorer and existing conservation methods are far from perfect. SANDRA WILLIGER, CONSERVATOR, STAINED GLASS CONSERVATION STUDIO, COLOGNE CATHEDRAL: “ It’s a bit difficult for the restorer to say we must use that product to protect the glass…knowing in a few decades the material will change. We use techniques that are not the best.we can do better but we rely on research and scientific development.” That is the aim of the European research project, Constglass. Its a place where research is carried out to assess the health of the stained glass while working on new restoration techniques. Some 200 kilometers from Cologne chemists and physicists analyse samples with modern techniques like red spectroscopy. Firstly the researchers check the damage due to corrosion, chemical attack, fungus and humidity in both the glass and in previous restoration materials. GERHARD SCHOTTNER, COORDINATOR, CONSTGLASS PROJECT: “ The historic stained glass window are important for our shared European history. And this project is a unique opportunity to analyse the materials used in the restoration of stained glass over the last 30 years and to discover if the attempts were successful. We can gather information, which will help us to avoid the problems faced by glass in France and England and other European countries. We can then remove materials and replace them with others we have developed here.” New restoration methods are applied to the surface of the glass. Electron microscopes are then used to see if the techniques halt the erosion. Researchers can then test the new methods at a chemical level and see how effective they are and if they can be reversed. GABI MAAS, PHYSICAL TECHNICAL ASSISTANT, FRAUNHOFER ISC : “We can work with this microscope with a very high resolution, so that we can observe the very small structures. This is important to visualise the fine cracks of the glass. You can see it here, in this image: Here you can recognise the cracks that we are interested in. And the newly developed consolidation material will fill these cracks.” Further research is being carried out in the Belgian city of Ghent which is home to many stunning stained glass windows…like these at St Bavons Cathedral. At the University of Ghent, physicists use Tomography to unveil the morphology of a sample of stained glass from the 13th century, restored 20 years ago. MANUEL DIERICK, PHYSICIST, CENTRE FOR TOMOGRAPHY, GHENT UNIVERSITY : “We can investigate if the sample is globally damaged or just small parts in the object have been damaged. Because we are able to investigate the inside structure, we can also study if the damage has also gone deep inside the object or just marginally on the outer surface of the object. In this case we can see that the glass itself is very homogenous, but that there are some air inclusions inside. And here in the outer edge you can see starts of corrosion. The corrosion layer has indeed a certain thickness, which is in this case relatively limited”. Researchers can also understand how old and new restoration methods behave between layers of glass. PATRIC JACOBS, HEAD OF DEPARTMENT OF GEOLOGY AND SOIL SCIENCE, GHENT UNIVERSITY: “The technique provides us with information on the weathering crust . How thick is the weathering crust? Is it still sticking to the glass or not? Is it flicking off the glass?. Another example: most of the time, during conservation, pieces of glass have been put together with glue or other consolidants to consolidate, to keep them together. Also these consolidants, and these glues, exposed to external weather, they deteriorate. These measurements provide priceless information for the conservationists. ULRIKE BRINKMANN, ART HISTORIAN & HEAD OF STAINED GLASS CONSERVATION STUDIO, COLOGNE CATHEDRAL: “ The knowledge and the images we provide the analytical research, the knowledge of the material and the transformation of the material leads us on in our work.” PATRIC JACOBS, HEAD OF DEPARTMENT OF GEOLOGY AND SOIL SCIENCE, GHENT UNIVERSITY: “Stained glass windows testify the skills of the craftsmen who worked on them in the XIII or XIV centuries. I think if there is a very expression of European integration and of the European cultural spirit, I think it is in Stained glass windows. So we should do everything it is possible to preserve them for the future”.