Abstract: A method for producing a transparent polycrystalline magnesia-alumina spinel body having high ultraviolet transmissivity and high strength and hardness characteristics is provided. A closed porosity body is formed from a spinel powder preferably having at least minimum purity characteristics. The closed porosity body can be formed by techniques including hot pressing and pressureless sintering. The closed porosity body is subjected to a hot isostatic pressure treatment to reduce residual porosity. The resulting body has high transmissivity of electro-magnetic radiation in the range between about 0.2 microns and about 6 microns and is resistant to abrasion or erosion, has high strength, and does not substantially deteriorate after exposure to ultraviolet light.