Measuring sidewall thickness of glass containers

Apparatus for measuring glass layer thickness in the sidewall of a glass container (22) in which a container is placed in a bath (26) of oil having an index of refraction matching that of the container outer sidewall surface. The body of the container is engaged within the bath to permit rotation while restraining lateral motion as the finish of the container is rotated. Light energy is directed though the bath and tangentially through the sidewall of the container so as to establish a pattern of light energy as a function of sidewall layer thickness, and layer thickness is determined as a function of such light pattern. As applied specifically to measuring thickness of the casing glass layer in a cased glass container in accordance with the preferred method of the invention, such casing glass thickness is determined as a function of the pattern in the light energy that emerges from the oil bath.