In the case of roughened quartz, Vitro-Skin and
Transpore correlations between the in vitro SPF and label values
can be established, but they are not 1:1. The slope of the linear
regression curves results higher than 1 (1.5; 1.55 and 5.9
respectively); probably the slope could be modified by applying
different quantities instead of 1 mg/cm2 as demonstrated by other
authors [13].