CaSnSiO5 (CSSO) is conventionally sintered at 1450 ◦C with εr ~10.9, τf ~ 35 ppm/◦C, Q × f ~ 43,600 GHz [28,29] and is therefore, an ideal base to begin the search for cold sintered silicates. However, initial cold sintering studies of CSSO were unsuccessful and hence, following work by Wang and co-workers [26,27], K2MoO4 (KMO) was used as a fluxing agent to encourage densification and to tune τf to near zero. The microstructure, Ag compatibility and microwave dielectric properties of CSSO-KMO composites were therefore, investigated followed by the design, fabrication and testing of a prototype microstrip patch antenna on substrates made from optimum compositions.