Average ionisation inferred for the r-process elements in groups I–III. These elements are likely to produce the strongest lines under LTE conditions. We show them as a function of the observed time post-merger. The ionisation states were calculated using the Saha equation, where we assume delectron density, n_e(t) = 10⁸ cm⁻³(t/1.5 days)⁻³ and the blackbody temperature evolution found for AT2017gfo (Sneppen et al. 2023b). The vertical blue and red vertical regions indicate the observations with X-shooter and other instruments (see the spectral series in Fig. 1). At certain temporal intervals, particularly at around 1 day post-merger, the r-process elements that dominate the opacity transition rapidly between ionisation states. For t ⪆ 5 days post-merger, NLTE-effects are likely to become important, implying that neutral, single-, and double-ionised species of these elements may be present (Pognan et al. 2022).