Next-generation telescopes need mirrors that are extremely stable, lightweight, and affordable. Semplastics has developed a novel, innovative ceramic material which is lightweight, low-cost, and ideal for application as a mirror substrate. High-thickness, high-stiffness objects with excellent dimensional stability, low density, and low coefficient of thermal expansion can be manufactured in one piece through our energy-efficient process. Semplastics is proposing to extend prior research and manufacturing process development to produce larger-scale circular mirrors. This innovation will reduce mirror costs per square meter by an order of magnitude over current approaches based on glass or glass-ceramic solutions. As a part of the Phase II effort, Semplastics will deliver to NASA four large mirrors (up to 0.6m in diameter), sealed to address the residual surface porosity using one of two different coating systems, with ground and polished surfaces. At the end of Phase II, we will have matured and developed our production processes such that we are ready to establish the capability to produce mirrors of one meter diameter or larger.