The historic environment undergoes cycles of material deterioration, and these processes have a powerful impact on the meanings and values associated with it. In particular, decay informs the experience of authenticity, as a tangible mark of age and ‘the real’. This article examines the intersection between material transformation, scientific intervention and cultural value. Drawing on qualitative social research at three Scottish historic buildings, we show that there are a complex range of cultural values and qualities associated with material transformation. Furthermore, we highlight how the use of science-based conservation to characterise, and intervene in, processes of material transformation can affect these values and qualities. We argue that it is necessary and important to consider the cultural ramifications of such interventions alongside their material effects. This requires a case-by-case approach, because the cultural values and qualities associated with material transformation are context-specific and vary with different kinds of monuments and materials. We conclude with a series of recommendations aimed at integrating humanities and science-based approaches to transformation in the historic environment.