The 68506 is a Tungar half wave rectifier designed for low voltage battery chargers. Tungar comes from the Tungsten filament and the Argon gas filling. The anode is graphite. The gas makes possible a low voltage drop across the rectifier, typically 10 Volts, but also limits the anode voltage.
Our other 68506 was branded Ediswan and is thus older than this exhibit where the company after merger was known as AEI. It also has clearer images of the internal structure as the internal coating was thinner.
See also The general Electric Tungar booklet.
All of the glass is silvered.
The GES base. The black disc is the anode and below can be seen the helical filament.
The balloon envelope is 81 mm in diameter, and including the GES base is 170 mm tall.
References: Datasheet. Type 68506 was first introduced in 1948.