Residuals to the local polynomial regression plotted in Fig. 1 as a function of GC absolute magnitude. Highly luminous clusters have larger residuals that increase with luminosity, while clusters less luminous than about −8 M_V display no correlation between scatter and luminosity. If the current luminosity of a GC correlates with its initial mass, this pattern can be interpreted as an effect of self-enrichment, that was effective only for clusters above a given mass threshold.