Influence of the commercial finishes of ornamental granites on roughness, colour and reflectance

Abstract

[Abstract] The effects of the four common commercial finishes (polished, honed, disc cutting and bush hammering) on several properties of ornamental granites were evaluated. Two granites of different texture, widely used as ornamental stones in NW Iberian Peninsula, were selected. Roughness, colour and reflectance (properties used as cleaning indicators of cultural heritage objects) of the surfaces subjected to each finish were characterized and the correlations among these parameters were obtained.

The results show that the roughness generated by disk cutting and polishing is higher in Vilachán than in Rosa Porriño, showing that the finer the grain size, the higher the roughness generated. The lightness parameter (L∗) in CIELAB space is dependent on the roughness of the surface. The rest of the colour parameters (a∗, b∗, C∗ab and hab) does not depend on roughness and they are related mostly with the colour of the surface by itself. Reflectance features are not affected by the different content of forming minerals and superficial colour which condition the reflectance intensity of each commercial finish. Reflectance is directly related with the roughness of the granite; the rougher the surface the higher the reflectance intensity. In addition, the lightness L∗ and the reflectance are directly related while the other colour parameters do not show any relation with the reflectance. These results can be used as an aesthetical criteria in order to standardize an objective methodology to evaluate the cleaning effectiveness in the conservation of cultural heritage objects.