Abstract: Method and apparatus for detecting "birdswing" flaws in glass containers. A container is illuminated using a beam of light introduced at its base. The column of light passes up through the container along its inner sidewall until it impinges upon a birdswing or like defect at the inner wall, which will cause light rays to be reflected through the outer wall. The light rays advantageously illuminate a zone at the base of the bottle which does not extend beyond the outer side wall, and are evenly distributed over a defined range of incident angles. Light reflected through the outer sidewall is detected as a bright spot by a suitable photodetector array, which monitors the entire container sidewall. This inspection technique effectively eliminates undesired indications of defects within the container wall, as well as of patterns embossed on the outer surface.