Controlled oriented crystallization of glass surfaces is desired for high precision applications, since the uppermost crystal layer significantly influences the properties of the material. In contrast to previous studies, the data presented here deal with separated crystals growing at defect-free surfaces in four atmospheres with different degrees of humidity (ambient/dry air, argon and vacuum). A glass with the composition 2 BaO–TiO₂–2.75 SiO₂ was heat-treated at 825 °C until fresnoite (Ba₂TiSi₂O₈) grew to a significant size. The crystal growth rate is found to increase with increasing humidity. The morphology of the crystals changes from highly distorted dendrites in the driest atmosphere (vacuum) to circular/spear-head-shaped crystals in the wettest atmosphere (ambient air), which we attribute to a decrease in viscosity of the glass surface due to water uptake. The least distorted crystals appear in the form of depressions of up to 6 µm. This has an influence on the observed crystal orientation, as measured by electron backscatter diffraction (EBSD). The pulled-in crystals change the orientation during growth relative to the flat glass surface due to an enrichment in SiO₂ at the crystal fronts. This confirms that the orientation of crystals is not fixed following nucleation.

The oxidation state control of polyvalent cations within materials is a pivotal determinant of their macroscopic properties and practical functionalities, from persistent and stress-stimulated luminescence, to energy storage and photocatalytic activity. Nonetheless, the resulting redox state is highly sensitive to synthetic conditions, and quantifying techniques aimed at its determination – while of the highest importance – remain constrained by practical challenges. In the present work, two simple and accessible wet-chemical methods, employing basic and easy-to-handle glassware and reagents, are introduced to address this issue. After validation on analytical standards encompassing diverse chemistries, they are applied to concrete off-stoichiometry materials of relevance – whether amorphous or crystalline – involving various redox couples and species, from highly reductive (Eu2+, Ti3+) to highly oxidizing (Ce4+, Tb4+). The roles of the host composition and processing conditions in altering the redox equilibria are discussed, and the obtained results are reinforced by the use of complementary analytical techniques. Multiple perspectives are emphasized, including the identification and resolution of the local environments and distributions of polyvalent cations, the isolation of high-valence species, and the provision of key insights into multifaceted phenomena for the design of advanced materials.