Ni/Fe abundance ratio for each clump in our sample of PNe. All the abundances have been calculated for T_e = 10 000 K and n_e = 1000 cm⁻³ and Chianty v10.1 atomic data for nickel. The dashed black horizontal line corresponds to the iron solar abundance from Lodders et al. (2009). Green and blue dots were estimated utilizing B15 atomic data, and the former account for fluorescence in nickel emission. Similarly, the pink and orange dots represent TZ18 atomic data.