To test whether the fluorescent liquid adsorbs onto the experimental surfaces, we first performed a “dry” and a lubricated friction experiment with one particular glass sphere. We then gently cleaned the used glass sphere, which was covered in fluorescent liquid, with EtOH and acetone. Subsequently, we again measured the dry friction between this sphere and a clean and dry glass substrate. The friction coefficient that we found was equal to that measured initially, confirming that there was no adsorbed layer of fluorescent liquid left that influenced the sliding. The same experiment for PS-on-glass contacts gave the same result.