Optical sample characterization facilitates measurement and testing at any angle in a full range of angles of light propagation through an optical sample, such as a coated glass plate, having a higher than air index of refraction. A rotatable assembly includes a cylinder having a hollow, and a receptacle including the hollow. The receptacle also contains a fluid with a known refractive index. An optical light beam is input normal to the surface of the cylinder, travels through the cylinder, then via the fluid, to the optical sample, where light beam is transmitted and/or reflected, then exits the cylinder and is collected for analysis. Due at least in part to the fluid surrounding the optical sample, the optical sample can be rotated through a full range of angles (±90°, etc.) for full range testing of the optical sample.