Abstract The late-nineteenth century saw a flourishing of mosaic in British architecture. Both traditional and innovative methods of mosaic-making were deployed in a wide variety of contexts from the 1850s onwards: in domestic, public, sacred, and secular buildings; for interior and exterior decoration; at large and small scales. Widespread experimentation with new materials, facilitated by the affordability of energy-intensive manufacturing processes, was complemented by a growing body of scholarship on the history of mosaics. Opus sectile was a novel type of opaque glass for mosaic-making that was developed by glassmakers James Powell & Sons in the mid-1860s. This new material quickly gained in popularity and was used in a variety of architectural projects throughout the late-nineteenth and early-twentieth centuries (for a list see Dennis Hadley, Powell’s Opus Sectile Locations [Coventry: Tiles & Architectural Ceramics Society, 2018]). Through a discussion of the development of opus sectile and its use in the 1860s, 1870s, and 1880s, the article explores its place in a landscape of both technological innovation and stylistic revivalism.