To describe the environment of the Si tetrahedra, the usual notation is used: Si tetrahedra, which are linked to n other Si tetrahedra, are marked Qn. If some of these n tetrahedra are not SiO4 but AlO4, the environment is designated as Qn(mAl), where m is the number of Al tetrahedra. Although unresolved, the broad resonance seen in the 29 Si MAS NMR spectrum being centered at -75.5 ppm thus corresponded to a distribution of Q0, Q1 and Q2 environments . The 27 Al MAS NMR spectrum (Figure ) of the anhydrous slag was also made of broad contributions. The Czjzek model was used to fit the spectrum since it gives a good lineshape prediction for spectra of quadrupolar nuclei such as 27 Al in poorly ordered solids. This model gives an expression of the joint probability density function of the quadrupolar parameters and allows one to obtain the mean square of the quadrupolar product √〈𝑪 𝑸𝜼 𝟐 〉 through the adjustable parameter (Equation 1(1)):