Binder jet additive manufacturing (BJAM) holds promise for high-density processing of high-temperature ceramic materials. Understanding BJAM fundamentals, including spreading of thin powder layers, powder-binder interactions, and post-processing is critical to develop robust process parameters. Toward meeting these needs, the fabrication of an open-architecture BJAM testbed is presented. The testbed is then used to study BJAM spreading and jetting fundamentals, including the application of novel binder compositions for microstructural control. To probe the influence of powder characteristics and spreading parameters on layer density and homogeneity, the testbed is coupled with transmission x-ray imaging for spatially-resolved, non-contact powder layer density measurements. To explore the influence of binder composition on densification and part warping, a rapid ink development process is applied to synthesize custom polymer and reactive metal salt binder inks. Direct deposition of a reactive binder sintering aid via the BJAM testbed demonstrates densification control and sustained part strength of ceramic parts.