In general, the chemical attack of glass, operated by basic aqueous solutions, involves the dismantling of the glass network, by disruption of siloxanic bridges. The dissolution products, however, may react and form gels. This contribution aims at presenting emerging potentialities from the control of the gel chemistry, in turn depending on the adopted glass and the attacking solution. Alkali hydroxides (in solutions not exceeding 3M) do not determine a complete dissolution, but promote surface modifications of fine glass particles (<100 μm). The progression of gel formation, upon ‘curing’ at 40-80 °C, transforms suspensions into pseudoplastic pastes, which can be foamed by intensive mechanical stirring. Highly porous, open-celled foams may be obtained at nearly room temperature. Such low temperature foaming is advantageous, since soda-lime glass foams may be determined, by viscous flow sintering at much lower temperature (700 °C, instead of >850 °C) than with conventional method, involving gas release during the heat treatment.
The ‘decoupling’ of foaming and heat treatment is fundamental for the upcycling of glass residues (e.g. from the manufacturing of glass fibres) sensitive to devitrification upon sintering: the crystallization ‘freezes’ the cellular structure defined by means of intensive mechanical stirring of pastes. The process lead to an easy obtainment of glass-ceramic foams from ‘stoichiometric’ glasses (e.g. based on hardystonite, Ca2ZnSi2O7, or on the eutectic of wollastonite-diopside, CaSiO3-CaMgSi2O6) usable in bone tissue engineering. In this specific field, the alkali intake in the gel, from the attacking solution, may be prevented, by using ammonium  hydroxide-based as alternative activators.
A recent challenge, again in the field of glass residues, is represented by glasses leading to stable hydrated alumino-silicate gels. As an example, boro-alumino-silicate from discarded pharmaceutical vials poses the conditions for usable products, just after drying, even beyond constructions. In fact, pseudoplastic pastes, based on waste glass and TiO2, may be used for the development of photocatalytic porous supports, by direct ink writing. For the same application, alkaline activation may be used again for the functionalization of porous sintered supports, preliminarily shaped by other additive manufacturing technologies (stereolithography, fused deposition).