A gamma densitometer window comprises a plate of non-metallic, preferably gamma transparent, material. The window further comprises a metallic frame member fitted around the outer edge of the plate and adapted to pre-load the plate with a compressive stress that is sufficiently high such that the sum of the compressive stress, tensile stress and shear stress components generated in the plate under high-pressure conditions is always compressive. The window is fabricated by shrink fitting the metallic frame member around the outer edge of the plate at a shrink-fit temperature such that the metallic frame member applies a compressive stress to the plate at any temperature below the shrink-fit temperature.