Fig. 6

a Colour change (ΔE*) and b change in brightness (ΔL*) of the samples surface as a function of the artificial weathering time. The error bars show the 95% confidence interval. If no error bar is visible, the error is within the symbol size. c The change of the varnish surface area as a function of artificial weathering time. The data from one 1-month gabbro sample had to be corrected due to a ring artefact that occurred during the μCT measurements. The topside view with the ring artefact is displayed next to the corrected measurement. Note that there is no clear correlation between detectable changes of the surface area and the artificial weathering time, but on average a significant weathering effect is noticeable. d A plot of ΔE* against the changed area with the 86 and 95% covariance ellipse for the granophyre and gabbro samples, respectively, showing a clear positive correlation between both parameter for the gabbro samples