The secret of transparent ceramic is its extremely low porosity.
Ceramic consists of many billions of tiny crystals that are connected to one another by high temperatures of 1200-1800°C. After the ceramic is fired, a few pores remain between the crystals. Normal densely sintered technical oxide ceramics have about 1-2% porosity. In contrast to tableware, these ceramics are waterproof even without glaze and have much higher strength and hardness. However, ceramic remains a brittle material and the remaining pores or defects can reduce the strength.
The new transparent ceramic sintered almost pore-free not only has a higher strength but can also become transparent. Using a Mie simulation calculation, the graphic shows the light scattering from pores of different sizes in spinel ceramics 1 mm thick. Due to the scattering of light on pores, normal technical ceramic appears white. With an extremely low porosity of 0.01% the ceramic becomes transparent.
The manufacture of transparent ceramics requires special high-purity raw materials and new processing techniques. Transparent ceramic does not contain any glass that could close the pores, but is created through the complete compression of high-purity synthetic oxide powder.