Result of the fitting procedure of the turnover pressure, p_m, as a function of grain radius, r, for all SiO₂ samples using Eq. (17) (left, solid line), Eq. (18) (centre, dashed curve), and Eq. (20) (right, dash-dotted line), respectively. The fits were performed using the least-squares method and ignoring individual error bars. The turnover pressure values obtained by Method A were restricted by the condition ∆ = 0.4...0.6. The logarithmic residuals are illustrated in the lower panels, together with the individual ranges in p_m (Method A) or error bars (Method B) of the data points. The fit results are noted in the respective legend. The shaded regions illustrate the 1σ and 2σ uncertainties of the respective fits.