Chromaticism differentiations: How variegated homogeneous stones used in buildings can gain diversified aesthetic appeal

This manuscript presents the results of a research about the change in colour of five different dimension stones, which are worldwide used for cladding and paving, whenever undergoing different surface processings. Substantial changes of the surface features, such as roughness and gloss were measured and correlated with CIE colour parameters. A spectrophotometer has been used in this research to measure the colour coordinates in CIE L*a*b* and CIE L*C*h colour spaces of the stone samples, which have been surface-finished by using traditional methods (i.e. polishing and bush-hammering), advanced technologies (pure water-jet) and diamond-disc sawing. The results show that the variability of L*a*b* coordinates and chroma (C*), is much higher in some stone (Orosei Marble and Rosa Portogallo Venato) than in others (Bianco Carrara D, Verde Guatemala and Sardinian Basalt), as a result of different surface finishing. Hue (h) shows significant variation especially when Verde Guatemala is tested. Bush-hammering brings all the tested rocks to higher lightness (L*) values. When the total colour difference (ΔE*) is recorded, pure water-jetting preserves the original colour of stones similarly to the polishing with the exception of Orosei Marble. A direct correlation between ΔE* and mean average roughness (Ra) has been found. On the contrary, an inverse correlation between specular gloss values and Ra has been acknowledged. How the results can be used in practice is also explained.