Rafael Navarro, Lidia Catarino, Dolores Pereira, Francisco Paulo de Sá Campos Gil

Colour is an important parameter that must be taken into account if aesthetic homogeneity in both construction and restoration work is to be achieved. In serpentinites, the different degrees of serpentinization or carbonation can influence their final colour. Sunlight, especially ultraviolet (UV) radiation, is a common agent that can decay properties such as hue, lightness, and chroma, and can have a very significant effect on the ageing process of dimension stones. Testing the effects of UV radiation is fundamental for predicting how materials may behave upon exposure. In this work, the surface alteration of materials due to UV radiation by means of arc-xenon lamps was carried out to determine the degree of variation in colour parameters in serpentinites used as dimension stones. It was observed that the effect of UV radiation on the materials studied was low, and that the samples tended to darken and become yellow. Gloss was the parameter that varied the most, which decreased in all the cases analysed. Associations were observed between the loss of gloss and a decrease in some parameters such as open porosity, water absorption at atmospheric pressure and water absorption by capillarity (direct), bulk density and uniaxial compression strength (reverse). The mineralogical composition of the stone was the main factor that influenced the loss of gloss. This research highlights the importance of the detailed study of colour variation in dimension stones due to exposure to UV radiation. The incorrect assessment of the damage that could be caused by this agent can lead to severe aesthetic destruction that may result in expensive legal actions.