Non-LTE Na abundance variation with effective temperature in NGC 6397. Bullets represent the RGB stars that are analysed in this study (abundance based on 568.2/568.8 nm lines) and open diamonds the stars analysed in Paper I (Lind et al. 2009, abundance based on 818.3/819.4 nm lines). The studies have five targets in common. The grey shaded area illustrates, given a range of different initial Na abundances, the predicted evolution of the surface abundance based on a model with atomic diffusion and turbulence below the outer convective zone (Richard et al. 2005, model T6.0).