Porous glass
![Ternary Phase diagram in the sodium borosilicate system](/Images/godic/202502/03/Phasendiagramm_natriumborosilikat1105.jpg")
![Porous glass filled with water, sample about 1 mm thick, made by phase separation in a thermal gradient (high temperature on the right) of a sodium borosilicate glass, followed by acid leaching](/Images/godic/202502/03/WetPorousGlass1105.jpg")
![Same porous glass as above, but dry. The increased difference between the refractive indices glass/air as compared to glass/water is causing greater whiteness based on the Tyndall effect.](/Images/godic/202502/03/DryPorousGlass1105.jpg")
Porous glass is glass that includes pores, usually in the nanometre- or micrometre-range, commonly prepared by one of the following processes: through metastable phase separation in borosilicate glasses (such as in the system SiO2-B2O3-Na2O), followed by liquid extraction of one of the formed phases; through the sol-gel process; or simply by sintering glass powder.