Quantitative colour analyses using digital specification technique for Mármore Bege Bahia, a representative Brazilian ornamental limestone of breccia-like texture

Abstract

The authors have performed based on digital quantitative colour specification in whole rock and spots using a scanner, a computer, and original colour analysing software Wilbur for Mármore Bege Bahia, an ornamental limestone of breccia-like texture exploited in the centre-north region of Bahia, Brazil. The rock is characterised by light (B=83.4), vivid (S=10.8), and relatively homogeneous (sigma(H)=3.9; sigma(B)=6.5) yellow, tending slightly to orange (H=35.8). The whole rock colour variation is limited to within 10% in brightness, and the colours plotted on the SB (saturation-brightness) diagram constitute a linear trend, with a declination rate of -1.6. This phenomenon is common in minerals with highly developed cleavage and attributed to random reflection on rock surface and subsurface reflection in the mineral interior of calcite. The rock blocks extracted from the quarries commonly have a large number of cavities and the resin-fill technique is frequently applied. It is recommended that the resin colours be adjusted adequately according to the above-mentioned linear trend in order to make the patched limestone visually appear as the natural one.