We summarize the different features of the scalar mesons from QCD spectral sum rule analyses of the two- and three-point functions. The results do not favour the uu + dd interpretation of the broad and low mass σ(0.6), and the us resonance nature of the eventually observed κ(0.9) meson. We also discuss some OZI-violating and classic semileptonic and radiative decay processes which can reveal in a model-independent way the eventual gluon component σB of the σ. In a meson-gluonium mixing scenario, one also expects an observation of the KK final states from the σB which may compete (if phase space allowed) with the one from a low mass ss state assumed in the literature to be the SU(3) partner of the σ(0.6) if this latter is a uu + dd state.