[Hoop]

"So does someone have an answer to the poster's question - were they available in the 30s? I don't know."

Prior to WW2 a lot of glass was made using uranium, usually uranium dioxide. This helped produce a variety of colors and shines,

This practice was halted because of the war, but now helps date vintage glass.

Glass with uranium in it will glow when exposed to black light and is very distinctive. If you do not have a black light, many antique shops use them in displays and shouldn't mind checking your shift knobs.

So, yes, some were made in the 1930's and ... and generally are considered more desirable and valuable (of course).