The pictures in this article come from the BVWS DVD of the 1950s Mullard film.
The Nickel tube that formed the base for the oxide coated cathode was cut to length by machine. Operators then mounted the cathodes onto support frames and pushed them into spray booths. The spray coating was of Barium and Strontium carbonates as these are stable compounds when exposed to the atmosphere.
The actual emissive material required for the cathode was the oxides of both Strontium and Barium. As this was less stable when exposed to the atmosphere the final formation of the oxide cathode was completed during the final envelope pumping process.
Spray coating of cathodes