In the context of chemical durability studies of nuclear waste glasses, glass alteration rates in water are usually described as initial glass alteration rate (r0) and residual glass alteration rate (rr). The rr is lower than r0 by up to several orders of magnitude depending on the glass composition and environmental conditions. The consensus is that the primary mechanisms responsible for this rate drop are a reduction in chemical affinity for Si dissolution due to solution saturation limits, and a passivation mechanism imposed by the formation of an alteration layer (gel). Open questions remain about the domination of one effect over the other, the exact mechanisms of gel passivation and their evolution over time. These unknowns make the development of mechanistic models and prediction of rr over long term challenging. Therefore, in this study we aim to develop a deeper understanding of the process of maturation of the gel layer by studying the evolution of the structure of the gel layer, porosities, pore-size distributions, and diffusion of water and aqueous glass species. To do so, we study the glass powders altered for over 30 years with >80% gel layer using 17O isotope impregnation followed by NMR and water sorption isotherms. We compare these results to those acquired on glass powders altered for only a few days or weeks. This gives information about the rigidity and the reorganization capacity of the gel layer network. Additionally, we also use short-term and long-term static glass-alteration experiments at pH90°C 9 and 90°C on glass powders and monoliths of 5 different glass compositions. We characterize the altered monoliths using 10B – 18O tracing experiments and ToF-SIMS to get information about the retention of boron in the gel layer and its diffusion coefficient, and Spectroscopic Ellipsometry to study the potential gradients of porosity. We characterize the altered glass powders using TGA and NMR to estimate the porosity and study the evolution of the gel layer structure respectively. Furthermore, TEM studies on the gel layer could give information about the pore-size distributions. Data analysis, interpretation and confrontation of these results with existing mechanistic models for the prediction of rr should then enable us to fill the remaining gaps regarding the accountability for the evolution of the passivation effect of the gel layer.