[Arran]

The Rogers metal spray tubes had a thick coating covered with a layer of paint, the older ones were "S" series and colored grey, the newer ones with an octal base were "M" series. I don't know about the "S" series but the shielding was grounded through through pin #1 of the base on the "M" series tubes, just like a metal tube. The "S" series metal spray tubes were also used in the U.S by Grigsby Grunow "Majestic", although very briefly as they were introduced in 1931 and the company went bankrupt in 1933-34, in 1935 RCA introduced their metal octal line of tubes so the newly reincorporated "Majestic Radio and TV" switched to those.
I don't know who made the tubes for Grigsby Grunow but Rogers owned their own tube plant so they used the "M" series types in new radios until the 1942 model year. Whatever method they used to put it on there the coating would not peel off like the European types. Fortunately most will interchange with normal non metal spray tubes, like a 6K7M is the same as a 6K7, 6K7G, or 6K7GT. A 41M is the same as a 6K6G or 6K6GT.
Unfortunately because Rogers owned their own tube tube plant they also developed some special purpose types that have been out of production since the late 1950s at least. The most common of these were the 2X3 rectifiers, which was a half wave rectifier that was used in pairs. Another was a 20J8 mixer oscillator tube, those were used in a lot of sets around 1941-42. There were also the 6X6 magic eyes, those had a double shadow like some European types like the EM34, but those aren't necessary for the radio to work.
Regards
Arran