Cultural and architectural heritage conservation and restoration: which colour?

Colours play a crucial role in the field of architectural heritage. Colour analysis and colour rendition are involved in several critical facets of heritage preservation, conservation and restoration. These aspects are related to accurate documentation and an accurate representation of heritage artefacts and architectural works. The aim of this paper is to describe critical issues and open problems of the processes involved in this field. Documentation is performed in multiple ways, acquiring heterogeneous data ranging from archival images, photographs, drawings using various consumer or professional instruments (eg, digital cameras and spectrophotometers). The reliability of colour acquisition might be influenced by instrumental reasons (the technology used to acquire colour information), by environmental changes (architectural heritage surveys are often performed outdoors), by morphology (complex architectural objects are characterised by concavities and convexities which complicate the reflection evaluation), or by materials (showing different reflection, porosity and transparency indexes). Identification of materials, such as colorants, pigments and dyes, is also a vital process in the heritage field. Colour information could be used as an approach to the identification of materials, but these methods are still under development, and many issues need to be solved to achieve reliable results. Visualisation techniques of a heritage artefact also present the problem of the correctness of the colour representation. Several problems need to be faced in this context: the reliability of the acquisition, colour management of the rendering software, model complexity, and fragmentation of the devices upon which the model is visualised.