Formulating Angular Invariant Structural Colors for Sustainable Colorant-Free Glazes

Structural color has been attracting scientific and engineering attention in various fields of biology, photonics, nanotechnology, and meta-materials. It often requires precise control of the surface structure with relatively low-throughput synthesis methods, such as lithography and self-assembly of monodispersed particles. Here, we report the application of structural color in bulk glazes, a widely used coating material to decorate and protect buildings and ceramic wares, via conventional glazing methods of simply mixing and heat treatment. We demonstrated colorant-free glazes with colors ranging from blue, yellow, magenta, to black, which can completely eliminate the use of critical colorant elements (e.g., Co, Pr, and Nd, some of which may also be toxic) in the glaze industry. The structural colors in the formulated glazes show remarkable angular invariance, overcoming the major bottleneck of previous reports on structural colors based on a two-dimensional meta-structure. We attributed the colors to the nanoscale phase separation and the tunable bicontinuous microstructures with a characteristic length scale down to 30 nm and sub-10 nm nanoprecipitates as characterized by the state-of-the-art aberration-corrected cryo-transmission electron microscopy. The thermal regulation property can be further achieved by the different colored glaze. Our design rules for colorant-free photonic glazes could contribute to further development of the sustainable glaze industry and offer insights of utilizing the concept of structural colors in large-scale bulk applications with energy saving and environmental protection in a cost-effective way.