Within the output feature group, the fraction of underreacted material correlates with that of the δ-Al2O3 phases, with a coefficient of -0.96. In turn, the correlation between the amounts of δ-Al2O3 and of overreacted material is only 0.67. In very good accordance with FA observations, principal component analysis (PCA, see Table ) shows that the data explanation ability can reach 94.7% when using five principle components (PCs) for input. When using only four PCs, a value of 88.9% is achieved. For the output, two features reach 99.9% explainability, while one single feature would reach only 86.6%.