Fig. 5

Box plots showing a the global colour change, \(\Delta E^{*}_{ab}\), for samples treated with E5 and E25; b the arithmetic average height parameter, \(R_{a}\), for control samples, E5 samples and E25 samples; Measurements from the top face are shown in red circles and the bottom face are shown in blue squares , with outliers represented by hollow symbols . The box represents the interquartile range (25th–75th percentiles) and the whiskers are determined by the 5th and 95th percentiles. The median is represented by the horizontal line while the mean is indicated by \(\times\)