Sol-gel glazes - a safe glass and ceramics coloring approach

Major attention has been given to safety, environmental, and health hazard issues which arise from using toxic inorganic colorants and pigments in ceramic and glass technologies. A safe alternative is presented, wherein organic colorants approved for human use are entrapped within sol-gel aluminosilicate hybrid matrices and used for glazing porcelain ceramic and glass substrates. Among the colorants used are brilliant blue FCF replacing the toxic cobalt blue, curcumin replacing the toxic cadmium sulfide yellow, and a mixture of carmine and allura-red replacing the toxic cadmium selenide red. Additional advantages of the proposed approach are lowering of energy consumption, offering convenient and efficient recyclability of the colored glasses (thus also solving the current requirements for color-classified recycling), offering a huge library of thousands of organic colorants, opening for the artist and product designer a wide range of visual effects, and opening new artistic coloration methods to be explored. Full characterization was carried out including UV-vis spectroscopy, photoluminescence, topographic thickness analysis, wettability, SEM and XRD analyses, and FIB elemental analyses. The glazes are bright, of the order of 250 microns thick, crack free, chemically stable, with good adherence to both ceramic and glassy surfaces, and recyclable to the pure colorless ceramics or glass by heating. The potential for artistic applications, is demonstrated. Graphical Abstract Porcelain tile glazed with an aluminosilicate thick layer, doped with colorants safe for human use.