Colorimetry and permeametry applied to evaluation of dimension stones butterfly beige and butterfly green subject to accelerated aging

Abstract

The quartz-syenites with hypersthene commercially known as Butterfly Beige and Green, are extracted in Barra de São Francisco, Espirito Santo State - Brazil. In this work, along the accelerated aging test in chamber with SO2 saturated atmosphere were performed: color measurements (CIELab Standard - ΔE, ΔL, Δa, Δb and spectral reflectance) for quantification of the aesthetic changes caused by physical - chemical attack in the chamber and; monitoring permeability “C (Gas intrusion permeametry - Darcy‘s permeability constant) of the rock types. The aggressive chemical agent in the system is an SO2 photochemical product, the H2SO4 (sulfuric acid), and its purpose is to simulate reactions that occur during exposure of rocks to acid rain. This experiment resulted in significant aesthetic changes on Butterfly Green, because it is a dark rock, suffered a considerable color loss (ΔE = 3.87 after 100 cycles) getting lighter (ΔL after 100 cycles = 3.57), also due to the variations of “a, which showed its green (Δa = -0.45 after 100 cycles) and “b (Δb = 1.43 after 100 cycles) that defined the yellowing caused on rock surface, both supported by the higher reflectance between 550 and 590 nm. For the Butterfly Beige the alteration consequences were less harmful, because it have a clear tone, showed almost half of the variation in luminance (ΔL = 1.98 after 100 cycles) checked in Green. Changes in “a (Δa = -0.07 after 100 cycles) and “b (Δb = -0.93 after 100 cycles) showed that the rock was inside green and yellow field respectively. The mineral that most influenced these findings was the orthoclase identified both in the Butterfly Beige, as in Green. About the permeability, the Butterfly Green showed higher cumulative value (C = 0.0097) along the cycles in the chamber, followed by Butterfly Beige (C = 0.0095).