Colour degradation in medieval manuscripts

Illuminated in word and in image, medieval codices are some of the most beautiful testimonies of our European past. Throughout our research, we observed numerous examples of colour materials degradation and, we thus discovered that their future preservation is threatened. In this work we describe the main pathologies found in Romanesque collections and calculate their extent for three major monastic collections, produced in Portuguese Romanesque scriptoria. The degradation patterns found in Books of Hours, a recent investigation, are also discussed.Based on this information we critically assess some currently employed preservation treatments. The first question we discuss is: do we have to restore illuminations? The second is: how to stabilise the pictorial layers? And finally, what tools do we have to measure the impact treatments have on our perception of colours? We demonstrate that it is not possible to design and implement active conservation treatments ignoring the binding media and its impact in colour perception and colour paint durability.Finally, we conclude that conservation of medieval manuscript illuminations is a major challenge that may, now, be overcome by producing knowledge within interdisciplinary teams, creating a dynamic trans-disciplinary expertise. This allows knowledge to be available to various communities, which will include specialists as well as stakeholders, assuring sustainable preservation of this treasured heritage.