The ORP11 is a cadmium sulphide photosensitive resistor with the maximum sensitivity in the red/infra-red part of the spectrum.
The later ORP12 was made as a glass cup sealed with plastic and having wire leads.
The active material is seen as dark. The substrate is showing in an interdigital pattern. This gives increased length to the resistive material.
The thin glass tube envelope is 16 mm in diameter and, excluding the special base pins, is 46 mm tall.
Reference: Data-sheet. Type ORP11 was first introduced in 1959.